Full Citation: K. Raghavachari and J. B. Anderson, "Electron Correlation Effects in Molecules", J. Phys. Chem. 100, 12960–12973 (1996). DOI: 10.1021/jp953749i.

Discussed on January 30, 2019.

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Description

This article provides a state-of-art overview (at the time) of the different methods used to recover electron correlation, and their applicability. It introduces different kinds of electron correlation (right-left, in-out, angular, dynamical, non-dynamical). It focuses on wave function methods which build on the Hartree-Fock wave function, a common reference wave function for the ground state obtained variationally from the Hartree-Fock theory through a self-consistent field procedure. It lays out certain criteria for correlation-recovering methods, which address size-consistency and computational effectiveness with increasing system size. While it notes that it is desirable to obtain correlation energies variationally (like configuration interaction methods do), it also mentions the effectiveness of non-variational methods like perturbation, quadratic configuration interaction and coupled cluster theories which recover the correlation energies to a high degree of accuracy. It notes other methods (MCSCF, CASSCF) that include more reference wave functions (in the form of configurations built from, for example, the previously noted HF wave function), those that have little to no systematic error and hence can be used for benchmarking these correlation methods (quantum Monte Carlo methods), and other ways to improve correlation recovery within a correlation method (use of Brueckner orbitals, GVB theory, composite methods).

On the inclusion of quantum Monte Carlo, the authors treat it as a supplement to the non-stochastic methods discussed in depth. This topical feature is likely attributed to Anderson's contributions to the field of quantum statistical mechanics.

Keywords

Electron correlation; HF; size-consistency; single reference; multireference; quantum Monte Carlo; CI; QCI; Metropolis sampling; Bell labs; MP2; MP4; CCSD(T); G2; full CI