We discuss an extension of the Hylleraas configuration-interaction method by incorporation of an exponentially correlated term. The necessary unlinked one-center, three- and four-electron integrals are derived in a closed form. No three- or four-electron auxiliary integrals appear in the final expressions. The evaluation scheme is an extension of the recent development of Ruiz [J. Math. Chem. 46, 1322 (2009)]. The prescription of combining diverged integrals to retrieve a finite value is avoided in the present approach.

• Received 20 December 2011

DOI:https://doi.org/10.1103/PhysRevA.85.042512