[molpro-user] Variational CASPT2?

[José Cortés]

Dear MOLPRO users

I have a question about one option in the caspt2 module (rs2). According to
the manual (caspt2 seccion), if the IMP3=2 option is included in the input
file, after the caspt2 calculation convergence, a variational CI
calculation is performed using all the internal configurations and the
first-order wavefunctions of all states as a basis.

My question is, what is the justification for perform a variational CI
calculation using the CASPT2 wave functions as a basis?. I would greatly
appreciate if someone could provide the reference where this method is
explained or some another which apply this procedure in a particular
problem.

Regards

Jose Jara
Universidad Nacional
Autónoma de México
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