Pade approximants and many-body perturbation theory: an application to the CH+ion

Abstract

Pade approximants to the diagrammatic many-body perturbation expansion for electron correlation energies in molecules are discussed. The numerical convergence properties of the perturbation expansion and the Pade approximants which can be formed from it are compared. Calculations of the ground-state potential energy curve for the CH+ ion are reported. Systems, such as CH+, which contain low-lying excited states, can be handled by forming (2/1) Pade approximants from third-order calculations using 'shifted' denominators.