Comprehensive Basis-Set Testing of Extended Symmetry-Adapted Perturbation Theory and Assessment of Mixed-Basis Combinations to Reduce Cost

Hybrid orextendedsymmetry-adapted perturbation theory(XSAPT) replaces traditional SAPT's treatment of dispersion with better performingalternatives while at the same time extending two-body (dimer) SAPT to a many-body treatment of polarization using a self-consistent charge embedding procedure.The present work presents a systematic study of how XSAPT interaction energiesand energy components converge with respect to the choice of Gaussian basis set.Errors can be reduced in a systematic way using correlation-consistent basis sets,with aug-cc-pVTZ results converged within <0.1 kcal/mol. Similar (if slightly lesssystematic) behavior is obtained using Karlsruhe basis sets at much lower cost, andwe introduce new versions with limited augmentation that are even more efficient.Pople-style basis sets, which are more efficient still, often afford good results if a largenumber of polarization functions are included. The dispersion models used inXSAPT afford much faster basis-set convergence as compared to the perturbativedescription of dispersion in conventional SAPT, meaning thatcompromisebasis sets (such as jun-cc-pVDZ) are no longerrequired and benchmark-quality results can be obtained using triple-zeta basis sets. The use of diffuse functions proves to be essential,especially for the description of hydrogen bonds. Thedelta(Hartree-Fock)correction for high-order induction can be performed indouble-zeta basis sets without significant loss of accuracy, leading to a mixed-basis approach that offers 4xspeedup over the existing(cubic scaling) XSAPT approach.

Automated summary

This study systematically investigates the convergence of XSAPT interaction energies and energy components with respect to the choice of Gaussian basis sets. Errors can be reduced using correlation-consistent basis sets and new versions with limited augmentation. The use of Pople-style basis sets may afford good results if a large number of polarization functions are included.