Molcas Forum

marcalias

Member

Registered: 2021-09-20

Posts: 1

Minimum number of particles in RAS3

Dear Molcas users,

I have recently started to compute core-excitations and I would like to compute the Fe K-edge XANES for a first row mononuclear Fe(II) complex. Following the selection rules for the transition dipole moment, the main peak in this spectra should correspond to the 1s to 4p transition, therefore I want to include both set of orbitals in my restricted active space. The 4p orbitals are strongly mixed and are very diffuse, then a large number of virtual orbitals have to be included to ensure that the 4p are there.

My active space for the HS state is formed by:
RAS1: 1s orbital of the metal
RAS2: 3x metal t2g orbitals + 2x metal eg orbitals
RAS3: 33 virtual orbitals

I am limiting the max. number of holes to 1 in RAS1 and the max. number of particles in RAS3 also to 1 in a RASSCF(8,1,1;1,5,33).

I am using the HEXS keyword to limit the possible CSFs to those with a single occupation in the RAS1. This efficiently produce the core-excited states, but still 1825 highly excited CSFs are possible. Is there any way to limit the number of CSFs by imposing a minimum occupation of particles in RAS3 similar to the HEXS keyword for the maximum occupation for RAS1? I have also thought in GASSCF but I think that it is not supported by RASSI.

Thank you in advance.

Sincerely,

Marc

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,085

Re: Minimum number of particles in RAS3

I don't think there is such a keyword. You could maybe use SUPSYM to prevent rotations of the 4p orbitals and so avoid including that many orbitals in RAS3, but you'd still need to give them some flexibility, or may sure they are reasonably optimized.