Thermochemical data from ab initio calculations. II. Total correlation energies, Schrödinger energies, and theoretical heats of formation

Abstract

AbstractBond correlation energies ϵ(XY) have been derived by partitioning second‐order Rayleigh–Schrödinger–Møller–Plesset (RSMP) correlation energies. Values of ϵ(XY) depend on the type of bonding between atoms X and Y. They can be considered as comprising correlation energies of bond, lone, and inner‐shell electron pairs of the group XY. Once a set of appropriate increments ϵ(XY) has been obtained, it is possible to estimate unknown RSMP energies of larger molecules. This concept also can be used when estimating total correlation energies E(CORR). For this purpose e(XY) values have been derived from known E(CORR) energies of small molecules. It is shown that ∣ϵ(XY)∣ increments increase linearly with the number n of electron pairs of the group XY. The function ϵ(n) becomes zero for n = 1/2 (one uncorrelated electron) and passes through −0.042 for n = 1, which is approximately the correlation energy of the bonding electron pair of H2 or a 1s inner‐shell pair. With the aid of estimated E(CORR) and HF limit energies, Schrödinger energies and theoretical heats of formation of relatively large molecules are obtained.