Abstract:
he present investigation reports on the prospect of usi
ng state specific multireference perturbation theory
(SSMRPT) with an improved virtual orbital complete ac
tive space configuration interaction (IVO-CASCI)
reference function (IVO-SSMRPT) to generate potential energy surfaces (PESs) for molecular systems
[such as CH
4
,C
2
H
6
,C
2
H
4
,H
2
O
2
, LiH, and KN] by stretching and breaking of suitable bonds with modest
basis sets. We have also revisited the dissociation energy profile of triplet ketene which exhibits a step-
like structure in the observed rate. The application of the method has also been made to the ionization
energies of H
2
O. Although the perturbative corrections are obtained by the diagonalization of the
effective Hamiltonian, in IVO-SSMRPT, only one physically relevant solution is achievable. It is parameter
free and does not require any threshold to avoid the intruder problem. It is strictly size-extensive and
size-consistent provided that local orbitals are used. The PESs obtained with our approach are smooth
all along the reaction path. Our estimates are in close agreement with the available reference data
indicating that IVO-SSMRPT is a robust paradigm for the accurate computation of ground, excited and
ionized states as it captures the mutual inter-play of different flavors of correlation effects in a balanced
and accurate way.
