# VANVLK: An algebraic manipulation program for canonical Van Vleck perturbation theory

## Description

Abstract Canonical Van Vleck perturbation theory is used to transform vibrational Hamiltonians to effective Hamiltonians, where the form of the effective Hamiltonian is better suited to the study of highly excited vibrational states of polyatomic molecules than that of the original representation. The key advantage is that the solution to the full problem is obtained in the new representation using significantly smaller basis sets than are needed to obtain the solutions in the original representation.... Title of program: VANVLK Catalogue Id: ABDQ_v1_0 Nature of problem VANVLK canonically transforms a Hamiltonian, expressed in normal form, to a new representation, where the solutions can be obtained using a significantly smaller basis set than is needed to obtain the solutions of the original representation. The information content is the same. This method allows considerable flexibilty in the choice of the final form of the Hamiltonian, and therefore alleviates the problems with divergences in perturbation expansions. The algebraic manipulation avoids the stor ... Versions of this program held in the CPC repository in Mendeley Data ABDQ_v1_0; VANVLK; 10.1016/0010-4655(88)90068-9 This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2019)