As Dr. Wilson explained to me, researchers had recently developed computational methods known as “local methods,” which made certain approximations to decrease the expense of working with larger molecules. In the description of space employed by local methods, electrons interact mainly with other electrons that occupy spatially close orbitals; with conventional methods, all electrons interact with each other. This approximation reduces the number of integrals the computational program has to evaluate, and thus reduces the computational cost. However, this also reduces the accuracy of local methods. I sought to discover whether local second second-order Moller-Plesset perturbation theory [LMP2] energies systematically converged to a CBS limit and to discover how the accuracy of LMP2 with respect to canonical MP2 varied across basis set levels, including at the CBS limit.

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• Chemistry