Exploring the Limits of Second- and Third-Order Møller-Plesset Perturbation Theory for Non-Covalent Interactions: Revisiting MP2.5 and Assessing the Importance of Regularization and Reference Orbitals

• Published in: Journal of chemical theory and computation Vol. 17; no. 9; pp. 5582 - 5599
• Main Authors: Loipersberger, Matthias, Bertels, Luke W., Lee, Joonho, Head-Gordon, Martin
• Format: Journal Article
• Language: English
• Published: 12.08.2021
• ISSN: 1549-9618; 1549-9626
• DOI: 10.1021/acs.jctc.1c00469

This work systematically assesses the influence of reference orbitals, regularization and scaling on the performance of second- and third-order Møller-Plesset perturbation theory wavefunction methods for non-covalent interactions (NCI). Testing on 19 data sets (A24, DS14, HB15, HSG, S22, X40, HW30, NC15, S66, AlkBind12, CO2Nitrogen16, HB49, Ionic43, TA13, XB18, Bauza30, CT20, XB51 and Orel26rad) covers a wide range of different NCI including hydrogen bonding, dispersion, and halogen bonding. Inclusion of potential energy surfaces from different hydrogen bonds and dispersion-bound complexes gauges accuracy for non-equilibrium geometries. 15 methods are tested. In notation where nonstandard choices of orbitals are denoted as method:orbitals, these are MP2, κ -MP2, SCS-MP2, OOMP2, κ -OOMP2, MP3, MP2.5, MP3:OOMP2, MP2.5:OOMP2, MP3: κ -OOMP2, MP2.5: κ -OOMP2, and κ- MP3: κ -OOMP2, κ -MP2.5: κ -OOMP2, MP3: ω B97X-V, and MP2.5: ω B97X-V. Furthermore, we compare these methods to the ω B97M-V and B3LYP-D3 density functionals as well as CCSD. We find that the κ -regularization ( κ = 1.45 a.u. was used throughout) improves the energetics in almost all data sets for both MP2 (in 17 out of 19 data sets) and OOMP2 (16 out of 19). The improvement is significant (e.g. the RMSD for the S66 data set is 0.29 kcal/mol for κ -OOMP2, versus 0.67 kcal/mol for MP2), and for interactions between stable closed shell molecules, not strongly dependent on the reference orbitals. Scaled MP3 (with a factor of 0.5) using κ -OOMP2 reference orbitals (MP2.5: κ -OOMP2) provides significantly more accurate results for NCIs across all data sets with non-iterative 𝒪( N 6 ) scaling (S66 data set RMSD: 0.10 kcal/mol). Across the entire data set of 356 points, the improvement over standard MP2.5 is approximately a factor of two: RMSD for MP3: κ -OOMP2 is 0.25 kcal/mol vs 0.50 kcal/mol for MP2.5. The use of high-quality density functional reference orbitals ( ω B97X-V) also significantly improves the results of MP2.5 for NCI over a Hartree-Fock orbital reference. All our assessments and conclusions are based on the use of the medium-sized aug-cc-pVTZ basis to yield results that are directly compared against complete basis set limit reference values.