Interaction energy decomposition methods: comparison and application to covalent interaction assessment

Since various interaction energy partitioning schemes yield different, basis-set-dependent components, we have analyzed several of them here using a wide range of even-tempered regularized basis sets reaching the Hartree-Fock limit. These results were subsequently compared with benchmark data generated by Symmetry-Adapted Perturbation Theory (SAPT). Our findings regarding the controversial polarization or charge-transfer term equivalents indicate that the delocalization $E_{\text{del}}^{\text{HVPT}}$ term defined within Hybrid Variation-Perturbation Theory (HVPT) and the polarization $E_{\text{pol}}^{\text{LMOEDA}}$ term in Localized Molecular Orbital Energy Decomposition (LMOEDA) coincide with the corresponding $E_{\text{ind,resp}}^{\left(20\right)}+E_{\mathrm{exch}\text{-}\mathrm{ind},\mathrm{resp}}^{\left(20\right)}+\delta E_{\text{int,resp}}^{\text{HF}}$ SAPT terms, saturating rapidly as the basis set size increases. In contrast, other charge-transfer terms-specifically $E_{\text{ct}}^{\text{KM}}$ from the Kitaura-Morokuma scheme, $E_{\text{ct}}^{\text{RVS}}$ from the Reduced Variational Space (RVS) method, and $E_{\text{CT}}^{\text{ALMO}}$ from the Absolutely Localized Molecular Orbitals (ALMO)-exhibit a much higher sensitivity to the basis set choice and tend to vanish in the large-basis-set limit. In addition, the ratio of the delocalization to electrostatic terms, $E_{\text{del}}^{\text{HVPT}}/E_{\text{el}}^{\text{HVPT}}$ , has been employed here to quantitatively analyze the potential covalent nature of the interactions within the active site of triosephosphate isomerase, aiming to evaluate the Zhang and Houk hypothesis, which attributes the catalytic power of extremely efficient enzymes to the covalent binding of the transition state.

SAPT calculations were performed using the MOLPRO package, whereas the HVPT, RVS, Kitaura-Morokuma, and LMOEDA results were generated using GAMESS (US). The ALMO interaction energy components were obtained using the Q-Chem software. Exponents for the s-type even-tempered regularized basis sets were generated according to the Schmidt-Ruedenberg scheme.