MOLPRO

21 MULTIREFERENCE RAYLEIGH SCHRÖDINGER PERTURBATION THEORY 170
21.3.2 Performing MS-MR-CASPT2 calculations
In the case of multi-state multi-reference CASPT2 calculations, only a single run is needed:
{RS2,MIX=nstates, options
STATE,nstates}
Example: MS-MR-CASPT2 calculation for LiF
r=[3,4,5,6,7,8,9,10] ang
i=1
geometry={Li
F,1,r(i)}
basis=vtz,F=avtz
hf
do i=1,#r
{multi
closed,3,0,0,0
occ, 5,2,2,0
state,2
canonical,ci}
{rs2,MIX=2
state,2}
e1_caspt2(i)=energy(1)
e2_caspt2(i)=energy(2)
!Hartree-Fock
!loop over range of bond distances
!SA-CASSCF for 2 states
!2-state CASPT2 with 2 reference states
!unmixed caspt2 energy for ground state
!unmixed caspt2 energy for ground state
e1_mscaspt2(i)=msenergy(1)
e2_mscaspt2(i)=msenergy(2)
enddo
!ms-caspt2 energy for ground state
!ms-caspt2 energy for excited state
{table,r,e1_caspt2,e2_caspt2,e1_mscaspt2,e2_mscaspt2
title,MS-MR-CASPT2 for LiF
plot,file=’lif_mr_mscaspt2.plot’
}
http://www.molpro.net/info/current/examples/lif_mr_mscaspt2.com
This produces the plot