Molcas Forum

Anugraha

Member

Registered: 2025-12-17

Posts: 24

Active space orbital rotation

Dear Molcas developres,

I am running a CASSCF(8,8) calculation on a planar molecule using cs symmetry. The active space consists of 4 pi , 3 pi star and 1 sigma star orbitals. My target states are S0, pi pi star and pi sigma star which are belonging to different irreducible representations under the symmetry constraint. When i did the SA-CASSCF calculation for the S0 and pi pi star state with ciroot = 2 2 1 the sigma star orbital went out of the active space and some orbital with unsual character came inside the active space of symmetry 1.

Therefore is it possible to do state averaging of states with different symmetries?
Or is there any way to maintain the sigma star orbital in the active sapce for the calculation of S0 and pi star state?

I would be really thankful if anyone can help me to resolve this issue.

Thank You
Anugraha

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,210

Re: Active space orbital rotation

It is currently not possible to have states of different symmetries in a SA. The way to "force" the sigma* orbital to stay in the active space would be to include enough states in your SA such that the sigma* has a non-negligible occupation.