Molcas Forum

dondai

Member

Registered: 2025-03-23

Posts: 2

Excited state energy within different symmetry orbitals

Hi,
I am trying to find vertical excitation energy of a molecule that is of Cs symmetry. The HOMO is of A symmetry and the LUMO if of A" symmetry. My question is, how can I constrain each of the symmetry orbitals to have 1 1 electrons, such that I get the first excited state for singlet, assuming my active space is 2 orbitals and 2 electrons? By writing CIROOT as 2 2 1, I only get 2 0  as occupation. With 3 3 1, it shows I cannot have more CIROOTS than possible, which I understand. I am aiming to get u d which I am unable to.

Sample input file

 &RASSCF
    Spin
      1
    Nactel
      2 0 0
    INACTIVE
     113 88               
    Charge
      0
    Ras2
      1 1
   CIROOT
    2 2 1

I understand that I can instead do a RASSCF calculation with C1 symmetry, but I am hoping to do state specific optimization SLAPAF for that specific excited state with the symmetry of the molecule as Cs. I find that the symmetry is broken when fixing group=C1 for the optimized orbital.

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,204

Re: Excited state energy within different symmetry orbitals

I guess you want "Symmetry = 2"? With two irreps, 20 and 02 belong to irrep 1, while ud belongs to irrep 2.

dondai

Member

Registered: 2025-03-23

Posts: 2

Re: Excited state energy within different symmetry orbitals

Thank you for your prompt reply, it worked.