# 4.2.20. GATEWAY¶

The Gateway module collects information about molecular system (geometry, basis sets, symmetry) to be used for future calculations.

Gateway module is a subset of SEWARD. All keywords for this module can also appear as an input for SEWARD, however, for clarity the information about molecular system can be placed as an input for this module. Note, that GATEWAY does not compute any integral, and so must be followed by run of SEWARD module.

GATEWAY destroys the communication file RUNFILE, if it is used in a combination with geometry optimization it should run outside the optimization loop.

## 4.2.20.1. Input¶

This sections will describe the various possible input blocks in GATEWAY. These control

the molecular structure (coordinates, symmetry and basis sets),

explicit auxiliary basis sets in terms of CD basis sets (aCD and acCD) or external auxiliary basis sets,

parameters for reaction field calculations, i.e. parameters for the Kirkwood model or the PCM model and options for Pauli repulsion integral and external field integrals,

options for finite nuclear charge distribution models in association with relativistic calculations, and

the option to use the Saddle method to locate transitions state geometries.

The GATEWAY input section always starts with the program reference:

```
&GATEWAY
```

### 4.2.20.1.1. General keywords¶

- TITLE
The keyword followed by a title.

- TEST
GATEWAY will only process the input and generate a non-zero return code.

- EXPErt
Activates “expert mode”, in which various default settings are altered. This will, for example, allow the user to combine relativistic and non-relativistic basis sets.

- BASDIR
The keyword allows to set up an extra location for basis set files. The value can be either an absolute path (started from /) or relative to submit directory, e.g. BASDIR=. In order to use a local copy of a basis set file with name FOO — place this file into directory specified in BASDIR

- BASLIB
The keyword followed by the absolute path to the basis set library directory. The default is the $MOLCAS/basis_library directory. Note that this directory must also be host to local copies of the .tbl files.

- RTRN
Max number of atoms for which bond lengths, angles and dihedral angles are listed, and the radius defining the maximum length of a bond follows on the next line. The latter is used as a threshold when printing out angles and dihedral angles. The length can be followed by Bohr or Angstrom which indicates the unit in which the length was specified, the default is Bohr. The default values are 15 and 3.0 au.

- ISOTopes
Specify isotopic substitutions or atomic masses. By default, the mass of the most abundant or stable isotope is used for each atom. With this keyword different isotopes or arbitrary masses can be chosen. The keyword is followed by the number \(n\) of isotopic specifications, and then by \(n\) lines. Each of these lines should contain the symmetry-unique index of the atom for which the default mass is to be modified and either the mass number of the desired isotope (tabulated masses for most known isotopes are available in the code, use

`0`

for the default isotope) or the desired mass in dalton, in the latter case the keyword Dalton should follow. Note that all atoms belonging to the same “center type” must have the same mass. This usually means all atoms of a given element with the same basis set. If more fine-grained specifications are wanted, additional center types must be created by using several BASIs Set blocks for the same element (native input) or by using labels (XYZ input).- ECPShow
Force GATEWAY to print ECP parameters.

- AUXShow
Force GATEWAY to print auxiliary basis set parameters.

- BSSHow
Force GATEWAY to print basis set parameters.

- VERBose
Force GATEWAY to print a bit more verbose.

### 4.2.20.1.2. Molecular structure: coordinates, symmetry and basis sets¶

There are three different ways to specify the molecular structure, symmetry and the basis sets in GATEWAY:

XYZ input,

the so-called native input (old Molcas standard).

Note that only XYZ input for GATEWAY is supported by Graphical User interface. GATEWAY makes a decision about the type of the input based on keywords. If Coord is used, it assumes that the input is in XYZ format.

The three different modes will be described below.

#### 4.2.20.1.2.1. Z-matrix and XYZ input¶

Some times it is more convenient to set up information about coordinates in a standard form of Z-matrix or Cartesian coordinates. In this case, the basis set for the atoms should be specified after the XBAS keyword. After that either ZMAT or XYZ should appear to specify the coordinates. Note that coordinates in these formats use ångström as units.

- XBAS
A keyword to specify the basis for atoms. The specification is very similar to the native format:

`ATOM.BasisSet`

. Each new atom is written at a new line. The end of the keyword is marked by an End of basis line.If all atoms have the same basis, e.g. ANO-S-VDZ, it is possible to use this name without element name. In this case there is no need to specify End of basis.

Example:

XBAS=STO-3G

or

XBAS C.STO-3G H.STO-3G End of basis

- ZMAT
Alternative format to give coordinates in terms of bond lengths, bond angles, and dihedral angles. Each line of a Z-matrix gives the internal coordinates for one of the atoms within the molecule with the following syntax:

**Name I bond-length J bond-angle K dihedral-angle****Name**is the label (atomic symbol + string) for a symmetry distinct center L;**I bond-length**distance of L from atom I;**J bond-angle**planar angle between atoms L–I–J;**K dihedral-angle**dihedral angle between atoms L–I–J–K.Note that the first atom only requires the

**Name**and defines the origin of Cartesian axis. The second atom requires**Name I bond-length**and it will define the Z axis. The third atom requires**Name I bond-length J bond-angle**and defines the XZ plane (and implicitly, the Y axis).Only numerical values must be used (no variable names) and ångströms and degrees are assumed as units.

Two types of special atoms are allowed:

*dummy***X**atoms and*ghost***Z**atoms. The former will appear in the calculations, they have a nuclear charge of 0 and have not electrons and Basis Set. They will also appear in the definition of internal coordinates in SLAPAF. The latter are used only within the Z-Matrix definition of the geometry but they will appear in the final Z-matrix section in SLAPAF. Both special atoms can be used to define the Cartesian axis and the symmetry elements.**End of ZMAT**or a blank line mark the end of the section.Here is an example for (S)-1-chloroethanol (\(C_1\) symmetry):

XBAS H.ANO-L...2s1p. C.ANO-L...3s2p1d. O.ANO-L...3s2p1d. Cl.ECP.Huzinaga.7s7p1d.1s2p1d.7e-NR-AIMP. End of basis ZMAT C1 O2 1 1.40000 C3 1 1.45000 2 109.471 H4 1 1.08900 2 109.471 3 120.000 Cl5 1 1.75000 2 109.471 3 -120.000 H6 2 0.94700 1 109.471 3 180.000 H7 3 1.08900 1 109.471 2 180.000 H8 3 1.08900 1 109.471 7 120.000 H9 3 1.08900 1 109.471 7 240.000 End of z-matrix

In geometry optimizations, SLAPAF will regenerate the coordinates as Z-matrix in the section with the summary concerning each iteration. This will be possible only if

*ghost*atoms are used within the first three atoms or if they are not used at all.Both BASIs and ZMAT keywords can be used at the same time. Here is an example for a complex between methanol and water (\(C_s\) symmetry):

Symmetry Y XBAS H.ANO-L...1s. C.ANO-L...2s1p. O.ANO-L...2s1p. End of basis ZMAT C1 O2 1 1.3350 H3 1 1.0890 2 109.471 H4 1 1.0890 2 109.471 3 -120. H6 2 1.0890 1 109.471 3 180. End of z-matrix Basis set O.ANO-L...2s1p. O -2.828427 0.000000 2.335000 / Angstrom End of basis Basis set H.ANO-L...1s. H -2.748759 0.819593 2.808729 / Angstrom End of basis

In this case SLAPAF will not regenerate the Z-matrix.

- XYZ
The keyword is followed by XYZ formatted file (a reference to a file), or file, inlined into the input.

Example:

XBAS=STO-3G XYZ=$CurrDir/Water.xyz

or

XBAS=STO-3G XYZ 1 note Angstrom units! C 0 0 0

Currently, the XYZ keyword does not operate with symmetry, and the calculation is always performed without symmetry.

#### 4.2.20.1.2.2. Advanced XYZ input¶

If the geometry is specified in XYZ format, all atoms should be specified. The default units are ångströms. By default, maximum possible symmetry is used.

“Molcas XYZ” file format is an extension of plain XYZ format.

First line of this file contains the number of atoms.

Second line (a comment line) can contain “a.u.” or “bohr” to use atomic units, instead of default ångströms. Also this line can contain keyword TRANS, followed by 3 numbers, and/or ROT, followed by 9 numbers (in this case coordinates will be Translated by specified vector, and/or Rotated), and SCALE (or SCALEX, SCALEY, SCALEZ) followed by a scale factor.

Remaining lines are used to specify Element and cartesian coordinates.

Element name might be optionally followed by a Number (e.g.

`H7`

), a Label (separated by`_`

sign: e.g.`H_INNER`

), or Basis Set (separated by`.`

, e.g.`H.STO-3G`

)

- COORD
The keyword followed on the next line by the name of an HDF5 (created by any module), or the name of an XYZ file, or inline coordinates in XYZ format. If the file is located in the same directory, where Molcas job was submitted there is no need to specify the PATH to this file. The keyword may appear several times. In this case all coordinate files will be concatenated, and considered as individual fragments.

- BASIS
The keyword can be used to specify global basis set for all atoms, or for a group of atoms. The keyword followed by a label of basis set, or by comma separated list of basis sets for individual atoms.

Note! The basis set definition in XYZ mode does not allow to use inline basis set.

Example:

COORD 4 C 0.00000 0.00000 0.00000 H 1.00000 0.00000 0.00000 H 0.00000 1.00000 0.00000 H 0.00000 0.00000 1.00000 BASIS STO-3G, H.6-31G*

In this example, the C atom (in the origin) will have the basis set STO-3G and the H atoms 6-31G*.

If keyword BASIS never appears in the input, the default basis, ANO-S-MB, will be used.

- GROUP
The keyword can be used to specify the symmetry of the molecule.

The keyword must be followed by one of:

FULL (default) — use maximum possible subgroup of \(D_{2h}\)

NOSYM (same as E, or C1)

space separated list of generators: e.g. X XY (for more details see SYMMETRY keyword)

If XYZ input has been used in GATEWAY, a file with native Molcas input will be produced and stored in working directory under the name findsym.std.

Note that choosing XYZ input you are expecting that the coordinates might be transformed. It can be shown by the following example:

```
&gateway
coord
3
O 0 0 0
H 1.0000001 0 0
H 0 1 0.0000001
*nomove
*group=c1
```

The geometry of the molecule is slightly distorted, but within a threshold it is \(C_{2v}\). Thus by default (keywords nomove and group are not active), the coordinates will be transformed to maintain the highest possible symmetry. If keyword nomove is active, the molecule is not allowed to rotate, and a mirror plane \(xy\) is the only symmetry element. Since the third hydrogen atom is slightly out of this plane, it will be corrected. Only activation of the keyword group=C1 will ensure that the geometry is unchanged.

#### 4.2.20.1.2.3. Native input¶

If the geometry is specified in a native Molcas format, only symmetry inequivalent atoms should be specified. The default units are atomic units. By default, symmetry is not used in the calculation.

- SYMMetry
Symmetry specification follows on next line. There may be up to three different point group generators specified on that line. The generators of a point group is the minimal set of symmetry operators which is needed to generate all symmetry operators of a specific point group. A generator is in the input represented as a sequence of up to three of the characters x, y, and z. The order within a given sequence is arbitrary and the generators can be given in any sequence. Observe that the order of the irreps is defined by the order of the generators as (\(E\), \(g_1\), \(g_2\), \(g_1g_2\), \(g_3\), \(g_1g_3\), \(g_2g_3\), \(g_1g_2g_3\))! Note that \(E\) is always assumed and should never be specified.

Below is listed the possible generators.

**x**— Reflection in the \(yz\)-plane.**y**— Reflection in the \(xz\)-plane.**z**— Reflection in the \(xy\)-plane.**xy**— Twofold rotation around the \(z\)-axis.**xz**— Twofold rotation around the \(y\)-axis.**yz**— Twofold rotation around the \(x\)-axis.**xyz**— Inversion through the origin.

The default is no symmetry.

- BASIs Set
This notes the start of a basis set definition. The next line always contains a basis set label. The basis set definition is alway terminated with the “End of Basis” keyword. For the definitions of basis set labels see the subsequent sections. Below follows a description of the options associated with the basis set definition.

**Label [/ option]**— The label is a specification of a specific basis set, e.g. C.ANO…4s3p2d., which is an ANO basis set. If no option is specified GATEWAY will look for the basis set in the default basis directory. If an option is specified it could either be the name of an alternative basis directory or the wording “Inline” which defines that the basis set will follow in the current input file. For the format of the**Inline**option see the section “Basis set format”. Observe that the label is arbitrary for this option and will not be decoded. The**Label**card is mandatory.**Name x, y, z (Angstrom or Bohr)**— This card specifies an arbitrary (see next sentence!) name for a symmetry distinct center and its Cartesian coordinates. Observe, that the name “DBAS” is restricted to assign the center of the diffuse basis functions required to model the continuum orbitals in R-matrix calculations. The label is truncated to four characters. Observe that this label must be unique to each center. The coordinate unit can be specified as an option. The default unit is Bohr. There should at least be one card of this type in a basis set definition.**Charge**— The real entry on the subsequent line defines the charge associated with this basis set. This will override the default which is defined in the basis set library. The option can be used to put in ghost orbitals as well as to augment the basis sets of the library. The**Charge**card is optional.**Spherical**[option] — Specifying which shells will be in real spherical Gaussians. Valid options are “all” or a list of the shell characters separated by a blank. The shell characters are s, p, d, f, etc. All shells after p are by default in real spherical Gaussians, except for the d-functions in the 6-31G family of basis sets which are in Cartesian. The**Spherical**card is optional. The s and p shells and the d-functions of the 6-31G family of basis sets are by default in Cartesian Gaussians.**Cartesian**[option] — Specifying which shells will be in a Cartesian Gaussian representation. For syntax consult the corresponding**Spherical**keyword.**Contaminant**[option] — Specifying for which shells the contaminant will be kept. The contaminants are functions of lower rank which are generated when a Cartesian shell is transformed to a spherical representation (e.g. \(r^2=x^2+y^2+z^2\) for d-shells, p contaminants for f-shells, s and d contaminants for g-shells, etc.). Valid options are the same as for the**Spherical**keyword. The default is no contaminant in any shell. The**Contaminant**card is optional.**Muon**— Specifying that the basis set is muonic.**End of Basis set**— Marks the end of the basis set specification. This card is mandatory.

Example of an input in native Molcas format:

```
&GATEWAY
Title
formaldehyde
SYMMETRY
X Y
Basis set
H.STO-3G....
H1 0.000000 0.924258 -1.100293 /Angstrom
End of basis
Basis set
C.STO-3G....
C3 0.000000 0.000000 -0.519589 /Angstrom
End of basis
Basis set
O.STO-3G....
O 0.000000 0.000000 0.664765 /Angstrom
End of basis
End of input
```

Advanced keywords:

- SYMThreshold
followed by a real number — threshold for symmetry recognition (default is 0.01 Å)

- CSPF
Turn on the use of Condon–Shortley phase factors. Note that this changes the sign of basis functions, and orbital files will not be compatible with runs without this keyword, and orbital visualizations may be wrong!

- MOVE
allow to translate and rotate molecule in order to find highest possible symmetry. (this is a default for all groups, except of \(C_1\))

- NOMOVE
do not allow to transform coordinates while searching for highest group (default for \(C_1\) group)

- BSSE
followed by an integer. Indicates which XYZ-file that should be treated like ghost atoms.

- VART
Specifies that the energy should not be considered invariant to translations. Translational variance is detected automatically, but sometimes it may be useful to enforce it.

- VARR
Specifies that the energy should not be considered invariant to rotations. Rotational variance is detected automatically, but sometimes it may be useful to enforce it.

- NUMErical
Forces the calculation of numerical gradients even when analytic gradients are available.

- SHAKe
Randomly modifies the initial coordinates of the atoms, maintaining the input (or computed) symmetry. This can be useful to avoid a geometry optimization converging to a higher-symmetry saddle point. The maximum displacement per atom is read from the following real number. This number can be followed by Bohr or Angstrom, which indicates the unit in which the displacement is specified, the default is Bohr.

Example:

```
&GATEWAY
COORD
water.xyz
BASIS
STO-3G
```

or, in short EMIL notation:

```
&GATEWAY
COORD=water.xyz; BASIS=STO-3G
```

Coordinate file may contain variables, as demonstrated in an example:

```
>>FILE H2.input
2
scale $DD
H 0.35 0 0
H -0.35 0 0
>>EOF
>> FOREACH DD IN ( 0.9 1.0 1.1 )
&GATEWAY
COORD=$WorkDir/H2.input
BASIS=STO-3G
&SEWARD
&SCF
>>ENDDO
```

The atom name in XYZ file can contain an orbitrary label (to simplify assigning of different
basis sets). To indicate the label, use `_`

: e.g. `C_SMALL`

. The same label should be
defined in the basis section: `BASIS=C_SMALL.ANO-S-MB`

. The basis set label can be also
added into the name of an element:

```
COORD
1
O.ANO-S-VDZP 0 0 0
```

XYZ file can also contain information about point charges. There are three possibilities to
setup atomic charges in XYZ file. The main option is to use `Q`

as an element name, and in this
case the forth number, the charge, should be specified. Another possibility is to use element
names ended with minus sign. In this case, a formal charge for the element will be used.
E.g. `H-`

, `Li-`

, `Na-`

, `K-`

defines \(+1\) charge located in the corresponding location.
`Mg-`

, `Ca-`

— defines charge \(+2\), `Al-`

— \(+3\), `C-`

, `Si-`

\(+4\), for anions, `F-`

, `Cl-`

, `Br-`

, `I-`

defines \(-1\),
`O-`

, `S-`

— \(-2\). Finally, a label at the comment line of XYZ file — CLUSTER followed by
an integer number can specify how many atoms are “real”, so the rest will be treated as
charges with default values for this element.

### 4.2.20.1.3. Constraints¶

In case of optimizations with constraints these are defined in the GATEWAY input. For a complete description of this keyword see Section 4.2.52.4.1.

- CONStraints
This marks the start of the definition of the constraints which the optimization is subject to. This section is always ended by the keyword End of Constraints. This option can be used in conjunction with any definition of the internal coordinates.

- NGEXclude
This marks the start of the definition of additional restrictions for numerical differentiation. This section is always ended by the keyword End of NGExclude. The syntax of this section is like that of normal constraints, and the degrees of freedom specified here will be excluded from numerical differentiation (like phantom constraints). If a line containing only “Invert” is included inside the section, the definition is reversed and only these degrees of freedom are differentiated. NGEXclude is intended for use with the KEEPOldGradient keyword in ALASKA, and can be combined with CONStraints, which will further reduce the numerical differentiation subspace [29]. Note that the value assigned to the constraints in this section is unused, but a

`Value`

block must still be included.

### 4.2.20.1.4. Explicit auxiliary basis sets¶

The so-called Resolution of Identity (RI) technique (also called Density
Fitting, DF) is implemented in the Molcas package. This option involves the use
of an auxiliary basis set in the effective computation of the 2-electron
integrals. Molcas incorporates both the use of conventionally computed,
externally provided, auxiliary basis sets (RIJ, RIJK, and RIC types), and
on-the-fly generated auxiliary basis sets. The latter are atomic CD (aCD) or the
atomic compact CD (acCD) basis
sets, based on the Cholesky decomposition method. The externally provided
auxiliary basis sets are very compact, since they are tailored for special
wave function methods. However, they are not provided for all available valence
basis sets. The aCD or acCD RI auxiliary basis sets are a more general option and
provides auxiliary basis sets for any wave function model and valence basis set.
If MOLCAS_NEW_DEFAULTS is set to `YES`

, acCD RI (RICD)
will be enabled by default, it can be disabled with NOCD.

- RIJ
Use the RI-J basis in the density fitting (DF) approach to treat the two-electron integrals. Note that the valence basis set must have a supporting auxiliary basis set for this to work.

- RIJK
Use the RI-JK auxiliary basis in the density fitting (DF) approach to treat the two-electron integrals. Note that the valence basis set must have a supporting auxiliary basis set for this to work.

- RIC
Use the RI-C auxiliary basis in the density fitting (DF) approach to treat the two-electron integrals. Note that the valence basis set must have a supporting auxiliary basis set for this to work.

- RICD
Use the aCD or acCD approach [10] to treat the two-electron integrals. This procedure will use an on-the-fly generated auxiliary basis set.

- NOCD
Disable Cholesky decomposition. Useful in the case RICD has been made the default with MOLCAS_NEW_DEFAULTS.

- CDTHreshold
Threshold for on-the-fly generation of aCD or acCD auxiliary basis sets for RI calculations (default value 1.0d-4).

- SHAC
Skip high angular combinations à la Turbomole when creating on-the-fly basis sets (default off).

- KHAC
Keep high angular combinations when creating on-the-fly basis sets (default on).

- aCD basis
Generate an atomic CD (aCD) auxiliary basis sets (default off).

- acCD basis
Generate an atomic compact CD (acCD) auxiliary basis sets (default on).

### 4.2.20.1.5. Reaction field calculations¶

The effect of the solvent on the quantum chemical calculations has been introduced in Molcas through the reaction field created by the surrounding environment, represented by a polarizable dielectric continuum outside the boundaries of a cavity containing the solute molecule. Molcas supports Self Consistent Reaction Field (SCRF) and Multi Configurational Self Consistent Reaction Field (MCSCRF) calculations within the framework of the SCF and the RASSCF programs. The reaction field, computed in a self-consistent fashion, can be later added as a constant perturbation for the remaining programs, as for example CASPT2.

The purpose of this facility is to incorporate the effect of the environment (a solvent or a solid matrix) on the studied molecule. The utility itself it is not a program, but requires an additional input which has to be provided to the GATEWAY program. Two methods are available for SCRF calculations: one is based on the Kirkwood model, the other is the so called Polarizable Continuum Model (PCM). The reaction field is computed as the response of a dielectric medium polarized by the solute molecule: the solute is placed in a “cavity” surrounded by the dielectric. In Kirkwood model the cavity is always spherical, whereas in PCM the cavity is modeled on the actual solute shape.

The possible set of parameters controlled by input are:

the Kirkwood model,

the PCM model, and

one-electron integrals representing Pauli repulsion and external fields.

First a brief presentation of the Kirkwood and the PCM models.

#### 4.2.20.1.5.1. The Kirkwood Model¶

The Kirkwood model is an expansion of the so-called Onsager model where the surrounding will be characterized by its dielectric permitivity and a radius describing a spherical cavity, indicating where the dielectric medium starts. (Note that all atoms in the studied molecule must be inside the spherical cavity.) The Pauli repulsion due to the medium can be introduced by use of the spherical well integrals which are generated by SEWARD. The charge distribution of the molecule will introduce an electric field acting on the dielectric medium. This reaction field will interact with the charge distribution of the molecule. This interaction will manifest itself as a perturbation to the one-electron Hamiltonian. The perturbation will be automatically computed in a direct fashion (no multipole integrals are stored on disk) and added to the one-electron Hamiltonian. Due to the direct way in which this contribution is computed rather high terms in the multipole expansion of the charge can be afforded.

#### 4.2.20.1.5.2. The Polarizable Continuum Model, PCM¶

The PCM has been developed in order to describe the solvent reaction field in a more realistic way, basically through the use of cavities of general shape, modeled on the solute. The cavity is built as the envelope of spheres centered on solute atoms or atomic groups (usually, hydrogen atoms are included in the same sphere as the heavy atoms they are bonded to). The reaction field is described by means of apparent charges (solvation charges) spread on the cavity surface, designed to reproduced the electrostatic potential due to the polarized dielectric inside the cavity. Such charges are used both to compute solute-solvent interactions (modifying the total energy of the solute), and to perturb the molecular Hamiltonian through a suitable operator (thus distorcing the solute wave-function, and affecting all the electronic properties). The PCM operator contains both one- and two-electron terms: it is computed using atomic integrals already present in the program, through a “geometry matrix” connecting different points lying on the cavity surface. It can be shown that with this approach the SCF and RASSCF variational procedures lead to the free energy of the given molecule in solution: this is the thermodynamic meaning of the SCF or CI energy provided by the program. More precisely, this is the solute-solvent electrostatic contribution to the free energy (of course, other terms depending on solute atomic motions, like vibrational and rotational free energies, should be included separately); it can be used to get a good approximation of the solvation free energy, by subtracting the SCF or CI energy computed in vacuo, and also to compute directly energy surfaces and reaction paths in solution. On the other hand, the solute wave-function perturbed by the reaction field can be used to compute any electronic property in solution.

Also other quantities can be computed, namely the cavitation free energy (due the the work spent to create the cavity in the dielectric) and the dispersion-repulsion free energy: these terms affect only the total free energy of the molecule, and not its electronic distribution. They are collectively referred to as non-electrostatic contributions.

Note that two other keywords are defined for the RASSCF program: they refer to the CI root selected for the calculation of the reaction field (RFROOT), and to the possibility to perform a non-equilibrium calculation (NONEQ) when vertical electronic transitions are studied in solution. These keywords are referenced in the RASSCF section. To include the reaction field perturbation in a SCF, RASSCF, CASPT2 or RASSI calculation, another keyword must be specified (RFPERT), as explained in the respective program sections.

Complete and detailed examples of how to add a reaction field, through the Kirkwood or the PCM model, into quantum chemical calculations in Molcas is presented in Section 5.1.6 of the examples manual. The user is encouraged to read that section for further details.

#### 4.2.20.1.5.3. Input for the Kirkwood and PCM models¶

##### 4.2.20.1.5.3.1. Files¶

The reaction field calculations will store the information in the following files, which will be used by the following programs

- ONEINT
One-electron integral file used to store the Pauli repulsion integrals

- RUNFILE
Communications file. The last computed self-consistent reaction field (SCF or RASSCF) will be stored here to be used by following programs

- GV.off
Input file for the external program “geomview” (see Tutorial section “Solvent models”), for the visualization of PCM cavities

##### 4.2.20.1.5.3.2. Input¶

Below follows a description of the input to the reaction field utility in the GATEWAY program. The RASSCF program has its own keywords to compute reaction fields for excited states.

Compulsory keywords

- RF-Input
Activate reaction field options.

- END Of RF-Input
This marks the end of the input to the reaction field utility.

Optional keywords for the Kirkwood Model

- REACtion Field
This command is exclusive to the Kirkwood model. It indicates the beginning of the specification of the reaction field parameters. The subsequent line will contain the dielectric constant of the medium, the radius of the cavity in Bohrs (the cavity is always centered around the origin), and the angular quantum number of the highest multipole moment used in the expansion of the change distribution of the molecule (only charge is specified as 0, charge and dipole moments as 1, etc.). The input specified below specifies that a dielectric permitivity of 80.0 is used, that the cavity radius is 14.00 a.u., and that the expansion of the charge distribution is truncated after \(l=4\), i.e. hexadecapole moments are the last moments included in the expansion. Optionally a fourth argument can be added giving the value of the dielectric constant of the fast component of the solvent (default value 1.0).

Sample input for the reaction field part (Kirkwood model)

```
RF-Input
Reaction field
80.0 14.00 4
End Of RF-Input
```

Sample input for a complete reaction field calculation using the Kirkwood model. The SCF computes the reaction field in a self consistent manner while the MRCI program adds the effect as a constant perturbation.

```
&GATEWAY
Title = HF molecule
Symmetry
X Y
Basis set
F.ANO-S...3S2P.
F 0.00000 0.00000 1.73300
End of basis
Basis set
H.ANO-S...2S.
H 0.00000 0.00000 0.00000
End of basis
Well integrals
4
1.0 5.0 6.75
1.0 3.5 7.75
1.0 2.0 9.75
1.0 1.4 11.75
RF-Input
Reaction field
80.0 4.75 4
End of RF-Input
&SEWARD
&SCF
Occupied = 3 1 1 0
&MOTRA
LumOrb
Frozen = 1 0 0 0
RFPert
&GUGA
Electrons = 8
Spin = 1
Inactive = 2 1 1 0
Active = 0 0 0 0
CiAll = 1
&MRCI
SDCI
```

Optional keywords for the PCM Model

- PCM-model
If no other keywords are specified, the program will execute a standard PCM calculation with water as solvent. The solvent reaction field will be included in all the programs (SCF, RASSCF, CASPT2, etc.) invoked after SEWARD: note that in some cases additional keywords are required in the corresponding program sections. Some PCM parameters can be changed through the following keywords.

- SOLVent
Used to indicate which solvent is to be simulated. The name of the requested solvent must be written in the line below this keyword. Find implemented solvents in the PCM model below this section.

- DIELectric constant
Defines a different dielectric constant for the selected solvent; useful to describe the system at temperatures other that 298 K, or to mimic solvent mixtures. The value is read in the line below the keyword. An optional second value might be added on the same line which defines a different value for the infinite frequency dielectric constant for the selected solvent (this is used in non-equilibrium calculations; by default it is defined for each solvent at 298 K).

- CONDuctor version
It requires a PCM calculation where the solvent is represented as a polarized conductor: this is an approximation to the dielectric model which works very well for polar solvents (i.e. dielectric constant greater than about 5), and it has some computational advantages being based on simpler equations. It can be useful in cases when the dielectric model shows some convergence problems.

- AAREa
It is used to define the average area (in Å²) of the small elements on the cavity surface where solvation charges are placed; when larger elements are chosen, less charges are defined, what speeds up the calculation but risks to worsen the results. The default value is 0.4 Å² (i. e. 60 charges on a sphere of radius 2 Å). The value is read in the line below the keyword.

- R-MIn
It sets the minimum radius (in Å) of the spheres that the program adds to the atomic spheres in order to smooth the cavity surface (default 0.2 Å). For large solute, if the programs complains that too many sphere are being created, or if computational times become too high, it can be useful to enlarge this value (for example to 1 or 1.5 Å), thus reducing the number of added spheres. The value is read in the line below the keyword.

- PAULing
It invokes the use of Pauling’s radii to build the solute cavity: in this case, hydrogens get their own sphere (radius 1.2 Å).

- SPHEre radius
It is used to provide sphere radii from input: for each sphere given explicitly by the user, the keyword “Sphere radius” is required, followed by a line containing two numbers: an integer indicating the atom where the sphere has to be centered, and a real indicating its radius (in Å). For example, “Sphere radius” followed by “3 1.5” indicates that a sphere of radius 1.5 Å is placed around atom #3; “Sphere radius” followed by “4 2.0” indicates that another sphere of radius 2 Å is placed around atom #4 and so on.

Solvents implemented in the PCM model are

Name |
Dielectric constant |
---|---|

water |
78.39 |

dimethylsulfoxide |
46.70 |

nitromethane |
38.20 |

acetonitrile |
36.64 |

methanol |
32.63 |

ethanol |
24.55 |

acetone |
20.70 |

isoquinoline |
10.43 |

dichloroethane |
10.36 |

quinoline |
9.03 |

methylenchloride |
8.93 |

tetrahydrofuran |
7.58 |

aniline |
6.89 |

chlorobenzene |
5.62 |

chloroform |
4.90 |

ethylether |
4.34 |

toluene |
2.38 |

benzene |
2.25 |

carbontetrachloride |
2.23 |

cyclohexane |
2.02 |

heptane |
1.92 |

xenon |
1.71 |

krypton |
1.52 |

argon |
1.43 |

Sample input for the reaction field part (PCM model): the solvent is water, a surface element average area of 0.2 Å² is requested.

```
RF-input
PCM-model
Solvent
water
AAre
0.2
End of RF-input
```

Sample input for a standard PCM calculation in water. The SCF and RASSCF programs compute the reaction field self consistently and add its contribution to the Hamiltonian. The RASSCF is repeated twice: first the ground state is determined, then a non-equilibrium calculation on the first excited state is performed.

```
&GATEWAY
Coord
4
formaldehyde
O 0.000000 0.000000 -1.241209
C 0.000000 0.000000 0.000000
H 0.000000 0.949585 0.584974
H 0.000000 -0.949585 0.584974
Basis = STO-3G
Group = C1
RF-input
PCM-model
solvent = water
End of RF-input
&SEWARD ; &SCF
&RASSCF
nActEl = 4 0 0
Symmetry = 1
Inactive = 6
Ras2 = 3
CiRoot
1 1
1
LumOrb
&RASSCF
nActEl = 4 0 0
Symmetry = 1
Inactive = 6
Ras2 = 3
CiRoot
2 2
1 2
0 1
JOBIPH
NonEq
RFRoot = 2
```

Again the user is recommended to read Section 5.1.6 of the examples manual for further details.

### 4.2.20.1.6. Keywords associated to one-electron integrals¶

- FNMC
Request that the so-called Finite Nuclear Mass Correction, excluded by the Born–Oppenheimer approximation, be added to the one-electron Hamiltonian.

- WELL integrals
Request computation of Pauli repulsion integrals for dielectric cavity reaction field calculations. The first line specifies the total number of primitive well integrals in the repulsion integral. Then follows a number of lines, one for each well integral, specifying the coefficient of the well integral in the linear combination of the well integrals which defines the repulsion integral, the exponent of the well integral, and the distance of the center of the Gaussian from the origin. In total three entries on each line. All entries in atomic units. If zero or a negative number is specified for the number of well integrals a standard set of 3 integrals with their position adjusted for the radius of the cavity will be used. If the distance of the center of the Gaussian from the origin is negative displacements relative to the cavity radius is assumed.

- XFIEld integrals
Request the presence of an external electric field represented by a number of partial charges and dipoles. Optionally, polarisabilities may be specified whose induced dipoles are determined self-consistently during the SCF iteration. The first line may contain, apart from the first integer [nXF] (number of centers), up to four additional integers. The second integer [nOrd] specifies the maximum multipole order, or -1 signifying no permanent multipoles. Default is 1 (charges and dipoles). The third integer [p] specifies the type of external polarisabilities: 0 (default) no polarisabilities, 1 (isotropic), or 2 (anisotropic). The fourth integer [nFrag] specifies the number of fragments one multipole may contribute to (relevant only if polarisabilities are present). The default is 0, meaning that each permanent multipole is only excluded in the calculation of the field at its own polarisability, 1 means that one gives a fragment number to each multipole and that the static multipoles do not contribute to the polarising field within the same fragment, whereas 2 can be used in more complex situations, e.g. polymers, allowing you to specify a second fragment number so that junction atoms does not contribute to either of the neighbouring fragments. Finally, the fifth and last integer [nRead] (relevant only if Langevin dipoles are used) may be 0 or 1 (where 0 is default), specifying whether an element number (e.g. 8 for oxygen) should be read for each multipole. In that case the default radius for that element is used to determine which Langevin grid points should be annihilated. A negative element number signifies that a particular radius should be used for that multipole, in thousands of a Bohr (-1400 meaning 1.4 Bohr). Then follows nXF lines, one for each center. On each line is first nFrag+nRead (which may equal 0) integers, specifying the fragments that the multipole should not contribute to (the first fragment is taken as the fragment that the polarisability belongs to) and the element number. Then follows the three coordinates of the center, followed by the multipoles and polarisabilities. The number of multipole entries is 0 for nOrd=-1, 1 for nOrd=0, 4 for nOrd=1, and 10 for nOrd=2. The number of polarisability entries are 0 for p=0, 1 for p=1, and 6 for p=2. The order of quadrupole moment and anisotropic polarisability entries is xx, xy, xz, yy, yz, zz. If default is used, i.e. only specifying the number of centers on the first line, each of these lines will contain 7 entries (coordinates, charge, and dipole vector). All entries are in atomic units, if not otherwise requested by the Angstrom keyword that must be placed between nXF and nOrd. All these data can be stored in a separate file whose name must be passed as an argument of the XField keyword.

- SDIPole
Requests computation of velocity integrals. This is usually enabled by default.

- ANGM
Supplement ONEINT for transition angular momentum calculations. Entry which specifies the angular momentum origin (in au). By default this is enabled with the origin at the center of mass.

- OMQI
Supplement ONEINT for transition orbital magnetic quadrupole calculations. Entry which specifies the orbital magnetic quadrupole origin (in au).

- AMPR
Request the computation of angular momentum product integrals. The keyword is followed by values which specifies the angular momentum origin (in au).

- DSHD
Requests the computation of diamagnetic shielding integrals. The first entry specifies the gauge origin. Then follows an integer specifying the number of points at which the diamagnetic shielding will be computed. If this entry is zero, the diamagnetic shielding will be computed at each nucleus. If nonzero, then the coordinates (in au) for each origin has to be supplied, one entry for each origin.

- RX2C
Request the scalar relativistic X2C (eXact-two-Component) corrections to the one-electron Hamiltonian as well as the property integrals.

- RBSS
Request the scalar relativistic BSS (Barysz–Sadlej–Snijders) corrections to the one-electron Hamiltonian as well as the property integrals. The non-iterative scheme is employed for the construction of BSS transformation.

- NOAMfi
Explicit request for no computation of atomic mean-field integrals.

- AMFI
Explicit request for the computation of atomic mean-field integrals (used in subsequent spin–orbit calculations). These integrals are computed by default for the ANO-RCC and ANO-DK3 basis sets.

- EPOT
An integer follows which represents the number of points for which the electric potential will be computed. If this number is zero, the electric potential acting on each nucleus will be computed. If nonzero, then the coordinates (in au) for each point have to be supplied, one entry for each point. This keyword is mutually exclusive with EFLD and FLDG.

- EFLD
An integer follows which represents the number of points for which the electric potential and electric field will be computed. If this number is zero, the electric field acting on each nucleus will be computed. If nonzero, then the coordinates (in au) for each point have to be supplied, one entry for each point. This keyword is mutually exclusive with EPOT and FLDG.

- FLDG
An integer required which represents the number of points for which the electric potential, electric field and electric field gradient will be computed. If this number is zero, the electric field gradient acting on each nucleus will be computed. If nonzero, then either the coordinates (in au) for each point or labels for each atom center have to be supplied, one entry for each point. In case a label is supplied it must match one of those given previous in the input during specification of the coordinates of the atom centers. Using a label instead of a coordinate can e.g. be useful in something like a geometry optimization where the coordinate isn’t known when the input is written. This keyword is mutually exclusive with EPOT and EFLD.

- EMPC
Use point charges specified by the keyword XField when calculating the Orbital-Free Embedding potential.

- RF-Input
Specification of reaction field parameters, consult the reaction field section of this manual.

### 4.2.20.1.7. Keywords associated with nuclear charge distribution models¶

Input parameters associated with different models of the nuclear charge distribution. The default is to use a point charge representation.

- FINIte
Request a finite center representation of the nuclei by a single exponent s-type Gaussian.

- MGAUSsian
Request a finite center representation of the nuclei by a modified Gaussian.

### 4.2.20.1.8. The Saddle method for transition state optimization¶

The Saddle method [78] is a method to locate transition states (TS). The method, in practice, can be viewed as a
series of constrained optimization along the reaction path, which connects two starting structure (could be
the reactants and products of a reaction), to locate the region of the TS and a subsequent unconstrained optimization
to locate the TS. The only data needed for the procedure are the energies and coordinates of the two structures.
**Note** that this option will overwrite the
coordinates which have already been specified with the normal input of the molecular geometry. However, this does
not make that input section redundant and should always be included.

- RP-Coordinates
This activates the Saddle method for TS geometry optimization. The line is followed by an integer specifying the number of symmetry unique coordinates to be specified. This is followed by two sets of input — one line with the energy and then the Cartesian coordinates in bohr — for each of the two starting structures of the Saddle method. Note that the order of the coordinates must always match the order specified with the conventional input of the coordinates of the molecular system. Alternatively, two lines with the filenames containing the coordinates of reactants and products, respectively, (in XYZ format) can be given.

- NOALign
By default, the two starting structures are aligned to minimize the root mean square distance (RMSD) between them, in particular, the first structure is moved and the second structure remains fixed. If this keyword is given, the starting structures are used as given.

- ALIGn only
The two starting structures are aligned, but nothing more is done. An input block for SEWARD is still needed, but no integrals are computed.

- WEIGhts
Relative weights of each atom to use for the alignment and for the calculations of the “distance” between structures. The possibilities are:

**MASS**. This is the default. Each atom is given a weight proportional to its mass. Equivalent to mass-weighted coordinates.**EQUAL**. All atoms have an equal weight.**HEAVY**. Only heavy atoms are considered, with equal weights. Hydrogens are given zero weight.A list of \(N\) numbers can also be provided, and they will be used as weights for the \(N\) symmetry-unique atoms. For example:

WEIGhts 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0

will align only atoms 7–12 out of 16.

Note that, in any case, weights of 0 are likely to cause problems with constraints, and they will be increased automatically.

- SADDle
Step size reduction for each macro iteration of the saddle method. The value is given in weighted coordinates, divided by the square root of the total weight (see the WEIGHTS keyword). Default value is 0.1 au.

### 4.2.20.1.9. Geometry optimization using constrained internal coordinates¶

These keyword are used together with the GEO to optimize the relative position of two or more rigid fragments. The starting geometry can either be defined by supplying an xyz-file for each fragment using the keyword coord or by placing a file named $Project.zmt in a directory named $Project.GEO. The z-matrix should be in the following format:

```
O 0.982011 0 1
H 0.982013 0 104.959565 0 2 1
H 1.933697 1 107.655494 1 114.496053 1 2 3 1
O 0.988177 0 173.057942 1 -56.200750 1 4 2 3
H 0.979890 0 104.714572 0 179.879745 1 5 4 2
```

where the three columns of real numbers are internal coordinates, and the last three columns of integers indicate which other atoms that are used to define the coordinate. The type of coordinates from left to right are bond distances, bond angles and dihedral angels, both for the coordinates and the link. The column of integers just to the right of each coordinate indicate if this coordinate should be optimized or not (1 = optimize, 0 = do not optimize).

There are also two utility-keywords used to create a z-matrix or to write out a constraint-definition for SLAPAF and keywords to rotate and translate fragments. (See documentation for GEO for more details)

- HYPER
This keyword is used to specify that a geometry optimization with constrained internal coordinates shall be performed later, a z-matrix and a set of displaced geometries are therefore constructed. The keyword should be followed by three real numbers defining the maximum displacement for each coordinate type. The order from left to right is bond distances, bond angles and dihedral angles. To use default values for the parameters the mutually exclusive keyword geo should be entered instead.

- GEO
This keyword is used to specify that a geometry optimization with constrained internal coordinates shall be performed later, a z-matrix and a set of displaced geometries are therefore constructed. Default values of 0.15 Å, 2.5 degrees, and 2.5 degrees are used for the maximum displacement of bond distances, bond angles and dihedral angles respectively. To enter other values for the parameters the mutually exclusive keyword hyper should be used.

- OPTH
This keyword is used to define the specific details of the optimization algorithm used for the geometry optimization in constrained internal coordinates. This keyword should be followed by two to three lines of parameter. The first line should contain an integer indicating optimization type (1 = steepest descent, 2 = a mix of steepest descent and Newton’s method, and 3 = Newton’s method). The second line should contain a real number defining a step factor. This number is multiplied with the gradient to obtain the step length. For optimization type 2 a third line containing a real number that defines a gradient limit should be entered. This limit determines how large the gradient must be for the steepest descent algorithm to be used. When the gradient is smaller than this limit Newton’s method is used instead.

- OLDZ
This keyword is used both to start a new calculation from a user-defined z-matrix and to restart calculations. When using the keyword for a new calculation a directory $Project.GEO must exist and contain a file called $Project.zmt with a z-matrix in the format defined above. The directory must not contain any files with the suffix .info when performing a fresh calculation since these files contain restart information.

- ZONLY
This keyword is used to construct a z-matrix from a set of xyz-files (fragments) and store it in the directory $Project.GEO. The optimization parameters of the resulting z-matrix are set so that only coordinates linking fragments are set to 1 (= optimize coordinate).

- ZCONS
This keyword is used to define constraints from a set of xyz-files (fragments) on a form that could be supplied to the SLAPAF in order to keep the fragments rigid. The resulting constraints-file is named $Project.cns and stored in the directory $Project.GEO. The atom-numbers in this constraint-file will not match those of your original xyz-file and should not be used together with this. Instead a new xyz-file named cons.xyz is created and placed into the directory $Project.GEO, this has the proper numbering to use together with the constraints.

- ORIGIN
This keyword is used to translate and rotate a set of xyz-files. The keyword must be entered before the xyz-files is entered with coord. The keyword should be followed by two lines for each fragment in the input. The first row should contain 3 real numbers defining a translation (x, y, z), the second row should contain 9 numbers defining a rotation (row1, row2, row3 of rotation matrix). The keyword origin is mutually exclusive with the keyword frgm which is an alternative way to express the same rotations and translations.

- FRGM
This keyword is used together with the keywords rot and trans to define rotation and translation of a specific fragment. Frgm defines an active fragment (each xyz-file is considered a fragment, the files are numbered based on order of appearance in the input from top to bottom). The keyword must be entered before the xyz-file it is supposed to modify is entered with coord. Each occurence of frgm should be followed by either one of or both of the keywords rot and trans to define rotation and translation. This keyword is mutually exclusive with the keyword origin

- ROT
This keyword should be followed by nine real numbers defining the rotation for the fragment defined by the preceeding frgm. The numbers should be the nine elements of a rotation matrix listed with one full row at the time.

- TRANS
This keyword should be followed by three real numbers defining the translation for the fragment defined by the preceeding frgm. The numbers should be the x, y and z coordinates of the translation in that order.

Example of an input:

```
&GATEWAY
Title
Water Dimer
frgm=2
trans=3.0 0.0 0.0
Coord=water_monomer.xyz
Coord=water_monomer.xyz
Group=c1
basis=cc-pVTZ
hyper
0.2 3.0 3.0
opth
3
15.0d0
```

In this example a water dimer is constructed from a single monomer by translating it 3.0 Å with the keyword trans. An optimization in constrained internal coordinates using newtons method with a step-factor of 15.0d0 are prepared for. For more details on these optimization see the manual entry for the module GEO.

### 4.2.20.1.10. QM/MM calculations with Molcas/GROMACS¶

The following keywords apply to QM/MM calculations performed with the Molcas/GROMACS interface (see Section 4.2.14 for more details).

- GROMacs
Requests that the definition of the full QM+MM system should be imported from GROMACS. The keyword should be followed by one of the options SIMPLE or CASTMM on the next line. In the case of SIMPLE, all MM atoms defined in the GROMACS input will be treated as

*outer*MM atoms in Molcas. This means, for example, that in a geometry optimization, their positions will be updated using microiterations rather than the conventional optimization scheme. Conversely, CASTMM requests that certain MM atoms should be treated as*inner*MM atoms in Molcas. Their positions will be updated with the same scheme as used for the QM atoms. The CASTMM option should be followed by two additional input lines, the first one containing the number of MM atoms to convert from outer to inner type, and the second containing a list of those atoms (using their corresponding GROMACS indices).- LINKatoms
Defines link atoms for use with the Morokuma updating scheme. The desired number of link atoms should be given as an integer on the next line. This should be followed by additional input lines, one for each link atom to be defined. Each definition should be of the form ILA, IQM, IMM, SCALE, where ILA, IQM and IMM are the GROMACS indices of the link atom and the corresponding QM and MM frontier atoms, respectively. SCALE is the scaling factor to be used in the Morokuma scheme. Note that each link atom must be defined as a QM atom in the GROMACS input. In addition, the frontier MM atom must be an inner MM atom specified as discussed above.