# 4.2.32. MCPDFT¶

The MCPDFT program in Molcas performs multiconfiguration pair-density functional theory (MC-PDFT) calculations, as described in [91][92]. The MC-PDFT method involves two steps: (i) a CASSCF, RASSCF, or GASSCF wave function calculation to obtain the kinetic energy, classical Coulomb energy, total electron density, and on-top pair density; (ii) a post-SCF calculation of the remaining energy using an on-top density functional. In the current implementation, the on-top pair density functional is obtained by “translation” (t) of exchange-correlation functionals. Four translated functionals are currently available: tLSDA, tPBE, tBLYP, and trevPBE, in addition to the “fully-translated” (ft) variants [93]: ftLSDA, ftPBE, ftBLYP, and ftrevPBE. As multiconfigurational wave functions are used as input quantities, spin and space symmetry are correctly conserved.

The molecular orbitals and one- and two-body density matrices are read from the JOBIPH (or JOBOLD) file generated during a RASSCF run.

## 4.2.32.1. Dependencies¶

To start the MCPDFT module, the one-electron and two-electron integrals generated by SEWARD are required. For MC-PDFT calculations it is suggested to use a fine or ultrafine grid via the following input specifications (see the SEWARD section for further details):

```
&SEWARD
grid input
grid=ultrafine
end of grid input
```

Additionally, a JOBIPH file must be supplied to provide the molecular orbitals and one- and two-body density matrices.

## 4.2.32.2. Files¶

### 4.2.32.2.1. Input files¶

MCPDFT will use the following input files: ONEINT, ORDINT, RUNFILE, JOBOLD, JOBIPH.

If Cholesky options are selected, additional Cholesky-related files will also be used. Only JOBIPH or JOBOLD is needed; the code will first look for JOBOLD first and JOBIPH second.

### 4.2.32.2.2. Output files¶

- JOBPDFT
- This file is written in binary format and has the same structue of the JOBIPH file.
- RUNFILE
- The RUNFILE is updated with information from the MC-PDFT calculation.
- MCDENS
- This ASCII file is generated for MC-PDFT calculations. It contains spin densities, total density and on-top pair density values on grid (coordinates in a.u.).

## 4.2.32.3. Input¶

This section describes the input to the MCPDFT program in the Molcas program system. The input starts with the program name

```
&MCPDFT
```

The KSDFT is the only required keyword.

- KSDFT
- The functional choice follows. Currently available functionals are: tPBE, tBLYP, tLSDA, trevPBE, tOPBE, ftPBE, ftBLYP, ftLSDA, ftrevPBE and ftOPBE.
- DFCF
- Use this keyword to scale the exchange terms and/or correlation terms of the functional requested. This keyword should be followed by the scaling factor for the exchange terms and the scaling factor for the correlation terms, separated by a space. If the values are 1.0 (default), then the original functional is used. For an HLE-type functional, use 1.25 (for exchange) and 0.5 (for correlation). Example: DFCF=1.25 0.5

### 4.2.32.3.1. Input example¶

The following example shows the input to the RASSCF and MCPDFT programs for a calculation on the water molecule. The tPBE functional is used. The calculation is performed in \(C_{2v}\) symmetry (symmetries: \(a_1\), \(b_2\), \(b_1\), \(a_2\), where the two last species are antisymmetric with respect to the molecular plane). Inactive orbitals are 1\(a_1\) (oxygen 1s) 2\(a_1\) (oxygen 2s) and 1\(b_1\) (the \(\pi\) lone-pair orbital). Two bonding and two anti-bonding \(\ce{OH}\) orbitals are active, \(a_1\) and \(b_2\) symmetries. The calculation is performed for the \(^1A_1\) ground state. Note that no information about basis set, geometry, etc. has to be given. Such information is supplied by the SEWARD integral program via the one-electron integral file ONEINT.

```
&RASSCF
Title= Water molecule. Active orbitals OH and OH* in both symmetries
Spin = 1
Symmetry = 1
Inactive = 2 0 1 0
Ras2 = 2 2 0 0
&MCPDFT
KSDFT=TPBE
```

The first RASSCF run is a standard CASSCF calculation that leads to variationally optimized orbitals and CI coefficients. The MC-PDFT run will use the orbitals and density matrices optimized during the preceding RASSCF run.