Molcas Forum

hbschlegel

Member

Registered: 2025-08-16

Posts: 2

CASPT2 and MCPDFT frequencies

Can openMolCAS calculate CASPT2 and MCPDFT frequencies?
If so, can you please provide a sample input? (with symmetry)

Thanks, Berny Schlegel

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,129

Re: CASPT2 and MCPDFT frequencies

It can, but...

a) The differentiation will be numerical or, at best, seminumerical. (For CASPT2 at least, fully numerical with symmetry, seminumerical without)
b) Only the symmetry-preserving displacements can be performed, so only the fully symmetric modes are reported.

H2O example:

&GATEWAY
  Coord = 3

    O      0.00  0.00  0.00
    H      0.56  0.75  0.00
    H      0.56 -0.75  0.00
  Basis = cc-pVDZ
  Group = Full
  RICD

> do while

&SEWARD

&RASSCF
  NActEl = 8
  Inactive = 1 0 0 0
  RAS2     = 3 2 0 1

&CASPT2
  IPEA = 0.0

&SLAPAF

> end do

&MCKINLEY

Same, without symmetry:

&GATEWAY
  Coord = 3

    O      0.00  0.00  0.00
    H      0.56  0.75  0.00
    H      0.56 -0.75  0.00
  Basis = cc-pVDZ
  Group = NoSym
  RICD

> do while

&SEWARD

&RASSCF
  NActEl = 8
  Charge = 0
  RAS2   = 6

&CASPT2
  IPEA = 0.0

&SLAPAF

> end do

&MCKINLEY