Molcas Forum

Tapan

Member

Registered: 2016-04-24

Posts: 6

RASSCF Syntax

&RASSCF
Title=  Water  molecule.  Active  orbitals  OH  and  OH*  in  both  symmetries
Spin  =  1
Symmetry  =  1
Inactive  =  2  0  1  0
Ras2  =  2  2  0  0 

The above code is taken from http://www.molcas.org/documentation/manual/node100.html.  I do not understand what is the SYMMetry here? Also, why are there 4 sets of integers for Inactive and RAS2?

Last edited by Tapan (2016-04-28 13:14:49)

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,079

Re: RASSCF Syntax

It is explained in that same page:

SYMMETRY: Specify the selected symmetry type (the irrep) of the wave function as a number between 1 and 8 (see SYMMETRY keyword in GATEWAY section). Default is 1, which always denote the totally symmetric irrep.

so, it is where you specify the "spatial" symmetry desired for your wavefunction, just like SPIN specifies the spin symmetry. If your molecule has no symmetry (group C1), or if you have specified that you want no symmetry restrictions in GATEWAY, then the only allowed value is 1 and it can be omitted (as in any other case, if you want the "most symmetric" wavefunction).

INACTIVE: Specify on the next line the number of inactive (doubly occupied) orbitals in each symmetry.

so, 4 numbers are for the 4 different symmetry irreps (in this particular case). The orbitals are sorted by symmetry, and you have to specify how many inactive ones you want in each group.