Theoretica chimica acta

, Volume 78, Issue 3, pp 175-187

First online:

A comparison of variational and non-variational internally contracted multiconfiguration-reference configuration interaction calculations

  • Hans-Joachim WernerAffiliated withFakultät für Chemie, Universität Bielefeld
  • , Peter J. KnowlesAffiliated withSchool of Chemistry and Molecular Sciences, University of Sussex

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access


The internally contracted multiconfiguration-reference configuration interaction (CMRCI) method and several non-variational variants of this method (averaged coupled pair approximation (ACPF), quasidegenerate variational perturbation theory (QD-VPT), linearized coupled pair many electron theory (LCPMET)) have been employed to compute potential energy functions and other properties for a number of diatomic molecules (F2, O2, N2, CN, CO) using large basis sets and full valence CASSCF reference wavefunctions. In most cases the variational CMRCI wavefunctions yield more accurate spectroscopic constants than any of the employed non-variational methods. Several basis sets are compared for the N2 molecule. It is found that atomic natural orbital (ANO) contractions led to significant errors in the computedr e , ω e , andD e values.

Key words

Variational Non-variational Configuration interaction Diatomic molecules