*NEVPT2 INPUT

Purpose:

Calculation of the second order correction to the energy for a CAS-SCF or CAS-CI zero order wavefunction. The user is referred to Chapter 19 on page  for a brief introduction to the $n$-electron valence state second order perturbation theory (NEVPT2).

.THRESH

Default = 0.0D0
READ (LUINP,*) THRNEVPT
Threshold to discard small coefficients in the CAS wavefunction

.FROZEN

Default = no frozen orbitals
READ (LUINP,*) (NFRNEVPT2(I),I=1,NSYM)
Orbitals frozen in NEVPT2 calculation

.STATE

No default provided
READ (LUINP,*) ISTNEVCI
Root number in a CASCI calculation. This keyword is unnecessary (ignored) in the CASSCF case.

Comments:

The use of canonical orbitals for the core and virtual orbitals is strongly recommended since this choice guarantees compliance of the results with a totally invariant form of NEVPT2 (see page ).

At present the NEVPT2 module can deal with active spaces of dimension not higher than 14.