Exploring the Limits of Second- and Third-Order Moller-Plesset Perturbation Theories for Noncovalent Interactions: Revisiting MP2.5 and Assessing the Importance of Regularization and Reference Orbitals

This work systematically assesses the influence of reference orbitals, regularization, and scaling on the performance of second- and third-order Moller-Plesset perturbation theory wave function methods for noncovalent interactions (NCIs). 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 NCIs including hydrogen bonding, dispersion, and halogen bonding. Inclusion of potential energy surfaces from different hydrogen bonds and dispersion-bound complexes gauges accuracy for nonequilibrium geometries. Fifteen methods are tested. In notation where nonstandard choices of orbitals are denoted as methods:orbitals, these are MP2, kappa-MP2, SCS-MP2, OOMP2, kappa-OOMP2, MP3, MP2.5, MP3:OOMP2, MP2.5:OOMP2, MP3:kappa-OOMP2, MP2.5: kappa-OOMP2, kappa-MP3: kappa-OOMP2, kappa-MP2.5: kappa-OOMP2, MP3:omega B97X-V, and MP2.5:omega B97X-V. Furthermore, we compare these methods to the omega B97M-V and B3LYP-D3 density functionals, as well as CCSD. We find that the kappa-regularization (kappa = 1.45 au 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 root-mean-square deviation (RMSD) for the S66 data set is 0.29 kcal/mol for kappa-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 kappa-OOMP2 reference orbitals (MP2.5:kappa-OOMP2) provides significantly more accurate results for NCIs across all data sets with noniterative 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 2: RMSD for MP3:kappa-OOMP2 is 0.25 vs 0.50 kcal/mol for MP2.5. The use of high-quality density functional reference orbitals (omega 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.

Automated summary

This work systematically assesses the influence of reference orbitals, regularization, and scaling on the performance of second- and third-order Moller-Plesset perturbation theory wave function methods for noncovalent interactions (NCIs). The study found that the use of kappa-regularization significantly improves energetics for both MP2 and OOMP2 methods, and that scaled MP3 using kappa-OOMP2 reference orbitals provides significantly more accurate results for NCIs. High-quality density functional reference orbitals also significantly improve the results of MP2.5 for NCI over a Hartree-Fock orbital reference.