Symmetry-Adapted Relaxation Theory (SART): Variational Embedding for Convergent Infinite-Order Induction without Overpolarization

Abstract

The induction part of intermolecular interaction energy describes the effect of the mutual polarization of subsystems. Low-order induction effects can be reasonably described by symmetry-adapted perturbation theory (SAPT), but the capture of important higher-order polarization effects requires the use of an external correction from supermolecular Hartree–Fock (HF) theory, which is not free from artifacts. When one describes induction through a response to an embedding potential representing the other molecule(s) (which is the case in a number of existing approaches such as the electrostatic embedding, Hartree–Hartree–Fock, and explicit polarization methods), it is easy to succumb to overpolarization unless the embedding potential fully accounts for the exchange effects, enforcing the Pauli exclusion principle and preventing a variational collapse to a Pauli-forbidden state. Here, we propose a new embedding framework that accounts for both electrostatic polarization and exchange effects in many-body systems. As a proof of principle, we apply the novel embedding potentials in a variational approach called symmetry-adapted relaxation theory (SART) that succeeds in recovering infinite-order induction energy from the HF method without a need to compute the HF wave function or energy of the entire complex. SART is expected to be the foundation for a new class of intermolecular perturbation theories, while the newly proposed potentials can also be applied to incorporate complete exchange into various embedding algorithms.