Constrained-Variation Method in Molecular Quantum Mechanics. Application to Lithium Hydride
Abstract
A general method is developed for calculating wavefunctions by minimizing the energy subject to the constraints of theoretically or experimentally known moments. The method is applied to a valence-bond type configuration-interaction wavefunction for LiH. An extremely small sacrifice in energy results when the wavefunction is constrained to fit the experimental dipole moment exactly. The expectation values of other physical properties are calculated both for the free-variation function and the constrained-variation function with the constrained-variation function yielding improved predictions for the diamagnetic shielding, diamagnetic susceptibility, and electric field gradient at the lithium nucleus. In addition, it exhibits better gauge invariance of the total susceptibility as well as improved adherence to the Hellmann—Feynman condition. New predictions of other properties which have not been determined experimentally are also calculated, including the electric quadrupole moment.
- Publication:
-
Journal of Chemical Physics
- Pub Date:
- March 1965
- DOI:
- 10.1063/1.1696255
- Bibcode:
- 1965JChPh..42.2124R