Molcas Forum

Lukhmanul Hakeem k

Member

Registered: 2024-02-05

Posts: 26

Clarification on CASSCF Single-Point Energy Calculation for A″ State

Dear Molcas developers,

I have a question regarding a CASSCF single-point energy calculation. I am interested in computing the S₃ excited state, which corresponds to a πσ* state of A″ symmetry. Since the molecule has Cs symmetry, I set Symmetry = 2 in my input.

Could you please confirm whether the following input is appropriate for correctly describing this state?

&RASSCF
Title
 Benzenemolecule.
Spin
    1
Symmetry
    2 
Nactel
    10 0 0 
Inactive 
    47 5 
Ras2 
    2 8
CiRoot 
    1 4; 4
LumOrb
ALTEr = 3; 1 48 52; 1 49 53; 2 5 6
&GRID_IT
  All

I would appreciate it if you could let me know whether this setup will correctly target the S₃ state of A″ symmetry.

Best regards,
Lukhmanul

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,129

Re: Clarification on CASSCF Single-Point Energy Calculation for A″ State

With that input, you're requesting the 4th root of the second irrep. The root number does not count the other irreps, so most likely that is not S_3. Also, you're requesting a state-specific calculation for a higher root, which is prone to root flips and convergence issues. Consider simply using "StAverage = 1" instead of CiRoot, and increase the number if you need to include more roots.

Lukhmanul Hakeem k

Member

Registered: 2024-02-05

Posts: 26

Re: Clarification on CASSCF Single-Point Energy Calculation for A″ State

Dear Sir,

Thank you for your response, and I apologize for the delayed reply. I have now carefully gone through the OpenMolcas manual.

My aim is to reproduce the reaction coordinate scans performed by Domcke and co-workers in their paper "Photoinduced Electron and Proton Transfer in Phenol and Its Clusters with Water and Ammonia."

From the paper’s computational methods, I understand that state-specific CASSCF (SS-CASSCF) is preferable for the excited-state optimizations. I already have the optimized ground-state geometry in the Cs point group.

I now plan to optimize the first two excited states of A′ symmetry using SS-CASSCF. For the first excited state (A′ symmetry), I am thinking of using the following input:

&RASSCF
Title
 Phenol molecule.
Spin
    1
Symmetry
    1
Nactel
    8 0 0
Inactive
    47 6
Ras2
    0 8
CiRoot
    1 2; 2
LumOrb

&GRID_IT
  All
For the second excited state (also A′ symmetry), I would change only the CiRoot line to:


CiRoot
    1 3; 3

For the first excited state with A″ symmetry, my planned input is:

&RASSCF
Title
 Benzenemolecule.
Spin
    1
Symmetry
    2
Nactel
    8 0 0
Inactive
    47 6
Ras2
    0 8
CiRoot
    1 1; 1
LumOrb

&GRID_IT
  All

I would be most grateful if you could kindly confirm whether these inputs are appropriate for my purpose, or if any modifications are advisable.

Thank you very much for your time and guidance. I truly appreciate your support.

Warm regards,
Lukhmanul Hakeem K.