Møller-Plesset (MP) perturbation theory is the simplest route for adding dynamical correlation to mean-field Hartree-Fock (HF). However, the practical utility of MP theory is severely constrained by limitations of HF orbitals. We examine whether density functional theory (DFT) optimized orbitals can be employed to improve the performance of MP theory at both the second (MP2) and third (MP3) order. We find that use of DFT orbitals leads to significantly improved performance for prediction of thermochemistry, barrier heights, non-covalent interactions, and dipole moments relative to standard HF based MP theory. Indeed MP3 (with or without scaling) with DFT orbitals is found to surpass the accuracy of coupled cluster singles and doubles (CCSD) for several datasets. We also find that the results are essentially functional agnostic in most cases, (although range-separated hybrid functionals with low delocalization error are somewhat more reliable on the whole). MP3 based on DFT orbitals thus appears to be an efficient, non-iterative O(N<sup>6</sup>) scaling wave function approach for single-reference electronic structure computations, indicating substantial promise for double hybrid DFT methods with MP3 correlation.

Making third order Møller-Plesset perturbation theory useful: The role of DFT orbitals.

ACS Spring Meeting 2021

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