Comparative Study of the Random-Phase Approximation, Hartree-Fock and Single Excited Configuration-Interaction Methods of Computing Excitation Properties of Some Molecules

Publisher Website
Google Scholar
Abstract
Selected excitation energies, potential surfaces of excited states, and oscillator strengths are computed using three methods: (1) the random-phase approximation (RPA), (2) the singly excited configurations-interaction (SECI) method based upon the ground-state restricted Hartree-Fock (RHF) determinant, (3) a variational or quasivariational method which is essentially an excited-state Hartree-Fock (HF) method and which is applied to each state of the system. The simplification of the intermediate neglect of differential overlap (INDO) method is used throughout and it seems not to affect the validity of the comparison of the different methods. The advantages and the disadvantages of respective methods are discussed. The molecules chosen for study are H2O, HCHO, CH2N2, and HCOOH. Conclusions are drawn on the basis of what are the most extensive set of semiempirical RPA calculations to date. The RPA method, within the approximations used and in the given examples, is found to have no advantages and to have several disadvantages relative to the conventional SECI method when static as opposed to dynamic properties are computed. This seems to be generally true for low-lying non-Rydberg molecular and atomic states.