Molcas Forum

Lukhmanul Hakeem k

Member

Registered: 2024-02-05

Posts: 45

Question about Using EXPBAS with 6-31+G** Basis Set

Dear Sir,

I am trying to optimize a molecule using CASSCF. When I select the active space with the STO-3G basis set, the orbital characters look as expected. However, when I switch to the 6-31+G** basis set, the orbital characters (especially the σ* orbitals) do not look correct compared to STO-3G.

In this situation, is it possible to use the EXPBAS tool to generate starting orbitals? The manual says EXPBAS is available only for ANO or CC basis sets, so I am not sure if it can be used with 6-31+G**.

Could you please advise me on the best way to transfer the STO-3G orbitals as an initial guess for 6-31+G**?

Thank you very much for your guidance.

Best regards,
Lukhmanul Hakeem K.

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,165

Re: Question about Using EXPBAS with 6-31+G** Basis Set

Not with EXPBAS. EXPBAS can only expand to a basis set that's a super set of the initial one.

But you can use the mort tool (in Tools/mort), if you have complied HDF5 support. Once you have your sto3g.rasscf.h5, do a GATEWAY+SEWARD calculation with 6-31+G**, copy the 631g.guessorb.h5 file as e.g. 631g.init.h5, and then run:

mort.py -f occupied sto3g.rasscf.h5 631g.init.h5

The 631g.init.h5 should now contain orbitals resembling the STO-3G calculation, which you can use as initial orbitals or a new CASSCF calculation.

Lukhmanul Hakeem k

Member

Registered: 2024-02-05

Posts: 45

Re: Question about Using EXPBAS with 6-31+G** Basis Set

Dear Sir,

Thank you for your kind response earlier. I tried to convert STO-3G orbitals to the 6-31+G** basis set using the mort.py tool as you suggested. However, I encountered the following error:

Error: Symmetry is not supported with --transfer

I used the command:

python mort.py -f occupied molcas_s3_222_opt.rasscf.h5 631g.init.h5

Please note that my STO-3G calculation was performed in Cs symmetry. Could this be the reason for the error? Does the mort.py tool only work when the calculations are done in C1 symmetry?

Thank you very much for your guidance.

Best regards,
Lukhmanul Hakeem K.

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,165

Re: Question about Using EXPBAS with 6-31+G** Basis Set

Right. You could first desymmetrize the STO-3G orbitals (-d flag) and then transfer them to 6-31+G**, but you'd have to do the latter calculation without symmetry too.

Lukhmanul Hakeem k

Member

Registered: 2024-02-05

Posts: 45

Re: Question about Using EXPBAS with 6-31+G** Basis Set

Dear Sir,

Thank you for your response. Actually, I would like to optimize the πσ* state in Cs symmetry. This state has A" symmetry, so keeping the symmetry is important in my case. Do you know of any alternative method that could be used for this situation?

Best regards,
Lukhmanul Hakeem K.

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,165

Re: Question about Using EXPBAS with 6-31+G** Basis Set

Use an ANO basis. You can use ANO-RCC-MB or ANO-R0 instead of STO-3G, they're both minimal bases, and ANO-RCC-VDZP or ANO-R1 should be roughly of 6-31+G** quality. You can selectively add/remove functions if you want.

Lukhmanul Hakeem k

Member

Registered: 2024-02-05

Posts: 45

Re: Question about Using EXPBAS with 6-31+G** Basis Set

Dear Sir,

Thank you very much for your suggestion. I will try it in my calculations.

Best regards,
Lukhmanul Hakeem K.