Molcas Forum

Anugraha

Member

Registered: 2025-12-17

Posts: 22

How to use 6-31+G** basis set in OpenMolcas

Respected OpenMolcas developers,

I am currently using OpenMolcas version 25.06, and I would like to use the 6-31+G** basis set. After looking through the basis set library, I realized that this basis set is not available directly.

It would be very helpful if someone could guide me on how to use the 6-31+G** basis set in OpenMolcas.

Thank you.

Anugraha

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,202

Re: How to use 6-31+G** basis set in OpenMolcas

Go to https://www.basissetexchange.org/
Select 6-31+G**, click on "Select All", select Format: Molcas basis_library, click on "Get Basis Set"
Save the basis in a new file, named for instance "6-31+Gpp" (don't use stars in the filename), by using either the "Download" or "Copy to Clipboard" button.
Create a file named "trans.tbl", in the same directory as the basis set file, with the contents below (first the "real" basis set name, then the actual filename)

6-31+G**    6-31+Gpp

(this is necessary whenever the filename does not match the basis set name in uppercase)
Add the BasLib keyword to GATEWAY, pointing to the directory where you have both trans.tbl and the basis set file:

&GATEWAY
  Coord = 3

    O 0.0 0.0 0.0
    H 1.0 0.0 0.0
    H 0.0 1.0 0.0
  Basis = 6-31+G**
  BasLib = $CurrDir

&SEWARD

jxzou

Member

Registered: 2020-09-11

Posts: 14

Re: How to use 6-31+G** basis set in OpenMolcas

Hi, Anugraha. Ignacio has provided an excellent and detailed solution. Here I want to show an alternative solution if you have performed any calculation using Gaussian/ORCA/PySCF  previously. That is to say, we can simply generate or dump the OpenMolcas .input file from Gaussian/ORCA/PySCF calculations, and with 6-31+G** basis set data automatically written.

Here is the Gaussian input file for the water molecule at the RHF/6-31+G** theory level,

%chk=h2o.chk
%mem=4GB
%nprocshared=2
#p RHF/6-31+G** 5D 7F nosymm int=nobasistransform

title

0 1
 O                 -4.34834106   -0.86492890    0.00000000
 H                 -3.38834106   -0.86492890    0.00000000
 H                 -4.66879565    0.04000693    0.00000000
[blank line]
[blank line]

After the Gaussian job is finished, we obtained the file `h2o.chk`. Now we can run

formchk h2o.chk
fch2inporb h2o.fch

Files `h2o.input` and `h2o.INPORB` will be generated. The 6-31+G** basis set data is well written in `h2o.input`.

If you do not have Gaussian, but have ORCA. We can also run

orca_2mkl h2o -mkl
mkl2inporb h2o.mkl

to transform ORCA wave function files to OpenMolcas files. `-dkh2` and `-sfx2c` arguments can be appended to `mkl2inporb h2o.mkl`, if you use any scalar relativistic Hamiltonian.

If you do not have Gaussian or ORCA, you can still use PySCF, e.g.

from pyscf import gto, scf
from mokit.lib import py2molcas

mol = gto.M(atom='''
O  -0.49390246   0.93902438   0.0
H   0.46609754   0.93902438   0.0
H  -0.81435705   1.84396021   0.0
''',
basis='6-31+G**')

mf = scf.RHF(mol).run()
py2molcas(mf, 'h2o.input')

By using these tricks, not only the previous calculation files are re-used, but also the calculation results between two programs can be easily compared.

Last edited by jxzou (2026-06-11 17:53:24)