Charge-Overlap Effects. Dispersion and Induction Forces

Abstract

For nondegenerate atom–atom and atom–ion interactions the long-range interaction energy is expressed as a sum of “nonexpanded” angular components. If charge overlap is neglected each of the nonexpanded energies goes to a well-defined limit; namely to one of the usual R−1-expanded induction or dispersion energies or else to zero (R is the internuclear separation). The R−1 expansions appear to be asymptotic expansions of the nonexpanded results and are valid only for large R. As specific examples the H–H+ and H–H interactions are considered as model systems for studying charge overlap effects in induction and dispersion forces. The calculations are carried out variationally using the complete discrete Laguerre functions of degree (2l + 2) as a radial basis set. The asymptotic nature of the R−1 expansions for these interactions is discussed by comparing the various expanded and nonexpanded results. The importance of the nonexpanded interaction energies is also discussed briefly in general.

A floating one centre perturbation treatment for H‐like molecules

“…The treatment gives the exact long range induction energies for large R and the exact united atom limit is obtained from E(O) as R -+ 0. Since this approach neglects electron exchange effects [7] the perturbation results represent the direct or Coulomb energy for the lsa state of H$ and therefore agrees with the average energy of the lso and 2po states of H$ for large R, see also Bibliography [ 101.…”

“…(1') Setting p = 0 and s = 1 yields the results of Bibliographies [6-81 which are exact for both large and small R. It is interesting to note [7] that the exact united atom limit for the electronic energy is obtained from (E'O) + E ( l ) + Ei2').…”

Reliable Gaussian basis sets for closed‐shell atoms

“…More sophisticated methods use individual damping factors for terms of different order in R -1. [34][35][36][37] In Table X …”

Gaussian representations of charge overlap effects in intermolecular forces

“…The purpose of this paper is to investigate the feasibility of using Gaussian basis sets for representing charge overlap effects [3] between the interacting species which are necessary for the calculation and the understanding of intermediate range interaction energies; see Bibliography [3-51 and the references therein. In this work atomic units are used throughout.…”