G2C4

G2C4 is an interface program between Gaussian and CFour (ver. 2.00beta or 2.1) via the External keyword of Gaussian. MRCC may also be used through CFour.

Recent Changes

09/19/2023

1. The script run-cfour.sh has been updated. The initial guess of Hartree-Fock may be read from an old JOBARC file by default to speed up SCF convergence.

04/21/2023

1. Bug fix for the ONIOM calculation by Gaussian 16.c.

11/18/2021

1. Reorder atoms back to the initial ordering if necessary.

2. Bug fix for the ONIOM EIn file by Gaussian 16.c.

02/25/2020

1. The first public version.

Compilation

> F90 -O3 g2c4.f90 -o g2c4.exe

where F90 can be gfortran, nvf90 (pgf90), ifort, or other Fortran 90 compilers.

How to run CFour in Gaussian

1. Put g2c4.exe as well as 3 templet files scripts/cfour.templet-* into a folder. For example, /home/myID/Chemsoft/G2C4

2. Put scripts/run-cfour.sh into your Gaussian calculation folder, and modify run-cfour.sh.

• Line 4 has to be modified if MRCC is going to be used,
• Lines 7 to 14 are related to CFour,
• Lines 16 to 29 are related to G2C4, where cfour_templet specifies the templet file used for CFour calculations. Change it to $g2c4dir/cfour.templet-ccsd, for example.

3. Don't forget to add the execute permission to run-cfour.sh: chmod +x run-cfour.sh

4. If necessary, modify the templet file, such as basis set, ECP, occupation, convergence criteria, and so on. The basis set and ECP files may also be defined in the lines 31 to 33 in run-cfour.sh.

5. Make a copy of test/opt-freq.inp in your Gaussian calculation folder, modify the path of run-cfour.sh in external= if necessary, and submit it as a Gaussian job.

Some tips

1. In the case of single layer system (i.e. without using the ONIOM keyword), the External keyword activates the geometry optimization procedure with MM microiterations, which converges quite slow. OPT(zmat) (for Z-matrix coordinates only!) and OPT(nomicro) converge much faster. The ONIOM calculation has no such a problem since redundand internal coordinates being used by default.

2. If both high and low layers in ONIOM are computed by CFour (or other external programs), Gaussian optimization procedure may report an error "MOMM, but no IMMCRS" in L103. You may use OPT(nomicro) or reset IOP(1/18) to 20 to solve the problem. For example, # ONIOM(External='./run-cfour-high.sh':External='./run-cfour-low.sh') IOP(1/18=20) OPT

Known problems

1. In the case of ONIOM by Gaussian 16.a (and maybe earlier revisions), OPT and FREQ have to be calculated separately through this interface.

2. If CFour cannot read ECPDATA defined by %ECPDATA=..., this file has to be provided in run-cfour.sh (line 33).