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Subsections

8.30 `MCPDFT`

The MCPDFT program in MOLCAS performs multiconfiguration pair-density functional theory (MC-PDFT) calculations, as described in [72,73]. 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[74] : 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.

8.30.1 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.

8.30.2 Files

8.30.2.1 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.

8.30.2.2 Output files

File Contents
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.).

8.30.3 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.

Keyword Meaning
KSDFT The functional choice follows. Currently available functionals are: tPBE, tBLYP, tLSDA, trevPBE, ftPBE, ftBLYP, ftLSDA, and ftrevPBE.

8.30.3.1 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: a₁, b₂, b₁, a₂, where the two last species are antisymmetric with respect to the molecular plane). Inactive orbitals are 1a₁ (oxygen 1s) 2a₁ (oxygen 2s) and 1b₁ (the $\pi$ lone-pair orbital). Two bonding and two anti-bonding OH orbitals are active, a₁ and b₂ symmetries. The calculation is performed for the ¹A₁ 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 preceeding RASSCF run.