Columbus Molcas Link

Introduction

A link between the COLUMBUS and OpenMolcas / Molcas programs is available since version 7.0. The interface works on several levels. MOLCAS may be used only for computing the atomic integrals allowing the computation of gradients, nonadiabatic coupling vectors, and spin-orbit coupling. Alternatively the RASSCF, CASPT2, and CC modules from OpenMolcas may be used in mixed calculations with programs from COLUMBUS.

Installation

Start with the installation of OpenMolcas and proceed to COLUMBUS.

OpenMolcas

COLUMBUS

Usage

Atomic integrals

The minimum input for an operational MOLCAS/COLUMBUS calculations must provide the MOLCAS input file named molcas.input which contains the SEWARD input section. This file can be created via colinp (using "Integral program input"). For more complicated inputs, it is advisable to consult the OpenMolcas manual. Note, that although the coordinates are specified in the molcas.input file, they are automatically substituted for those contained in the geom file. After initial provision of the molcas.input file you need to proceed with colinp, which upon selection of the MOLCAS integral code will automatically analyse molcas.input and write the appropriate COLUMBUS style input files.

For the computation of properties it has to be assured that MOLCAS computes the necessary integrals. Please enter the appropriate keywords into the SEWARD section of molcas.input .

Check the OpenMolcas manual for any details about keywords used.

Combining other MOLCAS and COLUMBUS modules

If other COLUMBUS and MOLCAS modules are to be combined, appropriate input sections in molcas.input have to be created. Use colinp to specifiy the kinds of calculations you want to perform.

A collection of example inputs is provided at $COLUMBUS/EXAMPLES/MOLCAS.

Operational details of the COLUMBUS driver runc

What modules of MOLCAS are actually invoked by runc is determined by the keywords seward,alaska,irasscf,rasscf,caspt2 in control.run. runc proceeds by first analysing the molcas.input file and extracting the appropriate input sections for the respective MOLCAS modules - in case of SEWARD the input section is updated for the current geometry as stored in the geom file. Thus, if you wish to do a series of single-point calculations with different geometries (of the same point group), provide a correspondingly modified geom file. Please note, that geom contains symmetry-redundant atoms while the SEWARD input contains the symmetry-non-redundant atoms, only. The redundant ones are automatically stripped from the contents of the geom file. The module specific input file is written to the WORK directory and runc calls molcas with this module specific input file. The necessary links to the MOLCAS standard file names are also automatically setup. (For MOLCAS users: the environment variables Project, WorkDir and CurrDir are set to 'molcas', $WORK and $JOBDIR, respectively.) MOLCAS output files can be found in the LISTINGS and WORK subdirectories of the current job directory.

The combination of MOLCAS integrals and e.g. RASSCF MOs is generally possible, since the integral transformation program tran can optionally read the MOLCAS orbital file format (tranin needs the keyword seward=1, lumorb=1 automatically supplied by runc).

Last change: April, 2021 (F. Plasser)