Theoretica chimica acta

, Volume 75, Issue 2, pp 111–127

Configuration-interaction energy derivatives in a fully variational formulation

  • Trygve Helgaker
  • Poul Jørgensen

DOI: 10.1007/BF00527713

Cite this article as:
Helgaker, T. & Jørgensen, P. Theoret. Chim. Acta (1989) 75: 111. doi:10.1007/BF00527713


A configuration-interaction energy function (Lagrange) which is variational in all variables, including the orbital rotational parameters, is constructed. When this Lagrangian is used for obtaining configuration-interaction derivatives, all the important simplifications which occur for derivatives of variational wave functions carry over in a straightforward way. In particular, the state and orbital rotational response parameters obey the 2n+1 rule and the Lagrange multipliers obey the somewhat stronger 2n+2 rule. The simplifications which are normally obtained by invoking the Handy-Schaefer technique are automatically incorporated to all orders. Simple expressions for energy derivatives up to third order are presented. The relationship between the numerical errors in the variational parameters and the errors in the calculated energy derivatives is discussed.

Key words

Energy derivativesVariational formulationConfiguration interaction

Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • Trygve Helgaker
    • 1
  • Poul Jørgensen
    • 1
  1. 1.Department of ChemistryAarhus UniversityAarhus CDenmark