We present a third-order perturbation correction to the regularized orbital-optimized second-order Møller-Plesset perturbation theory, κ-OOMP2, uniquely defined by applying Wigner’s 2n+1 rule with a regularized first-order wave function. The resulting sixth-order scaling electron correlation method does not diverge even in the presence of small energy denominators. This method, κ-OOMP2+MP3, was then examined on a thermochemistry dataset, W4-11. We optimized the scaling factors of 1.0 and 0.5 for the MP2 and MP3 correlation energies, respectively, across a wide variety of κ values. This method with the optimal scaling factors, κ-OOMP2+0.5MP3 was then tested against the two noncovalent interaction datasets, TA13 and S22, and one radical stabilization energy dataset, RSE43. Unregularized orbital-optimized scaled third-order Møller-Plesset perturbation theory (OOMP2.X) has been shown to perform well on these datasets. In these cases, κ-OOMP2+0.5MP3 shows little deviation from the performance of the unregularized method. Other tests on systems where conventional MP3 and MP2.5 have more difficulty, such as small gap systems and systems with significant spin-contamination at the Hartree-Fock level,<br/>will be presented as progress permits.

Regularized Møller-Plesset perturbation theory: Assessment of third-order perturbation theory on thermochemistry, bond dissociation, and noncovalent interactions

2019 Spring National Meeting

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