Molcas Forum

Lukhmanul Hakeem k

Member

Registered: 2024-02-05

Posts: 25

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: 1,124

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.