# 4.2.18. FALSE¶

FALSE is an interface module that allows using external programs to compute energies and gradients for geometry optimizations with SLAPAF. FALSE creates a text file with the current Cartesian coordinates, launches an external program (specified by the RUN keyword), and then reads an output text file and stores the information in the RUNFILE for SLAPAF to use. In a parallel environment, only the master process executes the external program (which can run on a different parallel environment).

Note that, even though the external program most likely does not use the integrals produced by SEWARD, SEWARD will still need to be run for every new geometry before FALSE to update the coordinates. It can, however, use a dummy basis set and/or the ONEOnly keyword.

FALSE can also be run in “add” mode, where the results from the external program are added to the existing values, instead of replacing them (see the MODE keyword). In this case, FALSE should be called after all desired energies and gradients have been calculated with some other method.

## 4.2.18.1. Files¶

$Project.false.in This file is generated by FALSE, and contains the current Cartesian coordinates of the system.$Project.false.out

This file should be generated by the external program, and contain the energy and possibly gradient and other properties.

## 4.2.18.2. Input¶

RUN

This is the only and compulsory keyword of the program. It specifies the executable to run the external program. The external program will be run as <program> <input> <output>, where <program> is the value of this keyword, and <input> and <output> are, respectively, $Project.false.in and$Project.false.out.

MODE

Specifies whether the values computed by the external program will replace any pre-existing values (REPLACE, which is the default), or they will be added as a new contribution (ADD). If set to ADD, and the output from the external program contains values for a single root, the values will be added to all roots.

## 4.2.18.3. Format¶

The format of the $Project.false.in file is simply the header [XYZ] followed by the Cartesian coordinates in xyz format (number of atoms, comment line, atomic symbols and coordinates in ångström). Example: [XYZ] 3 angstrom O -0.000000000000 0.000000000000 1.585980150915 H -1.441800130217 0.000000000000 -1.265660575457 H 1.441800130217 0.000000000000 -1.265660575457  The expected format for the$Project.false.out has sections marked by bracketed headers (case-insensitive), and all values are in atomic units. Unknown sections are ignored.

• [ROOTS] is compulsory, followed by the number of roots for which energies and other properties will be given later. If MODE is ADD, it should match the number of roots already existing, or be 1 (in which case the external contribution will be added to all roots).

• [RELAX ROOT] is optional, followed by the index of the root that will be optimized. If not given, the highest root will be assumed. If given, it must appear before other properties.

• [ENERGIES] is compulsory, followed by the energies of the specified roots in free format.

• [GRADIENT] is optional, followed by a root index and the Cartesian gradient of that root, in the order $$x$$, $$y$$, $$z$$ components of first atom, $$x$$, $$y$$, $$z$$ of second atom, etc. Numbers are in free format. This section can appear several times for different roots. If not present for the root to be optimized, numerical gradients will be computed.

• [NAC] is optional, followed by two root indices and the Cartesian nonadiabatic coupling vector for those two roots, in the same order as the gradient. Numbers are in free format. This section can appear several times for different root pairs.

• [HESSIAN] is optional, followed by a root index and the lower triangle of the Cartesian Hessian of that root, in row order (same component order as the gradient). Numbers are in free format. This section can appear several times for different roots.

• [DIPOLES] is optional, followed by the dipole moments ($$x$$, $$y$$, $$z$$ components) of the specified roots. The numbers are in free format, but the dipole for each root must start on a new line.

Example:

[ROOTS]
1

[ENERGIES]
-0.00023387481687211915