Multilevel DFT Response Theory

TL;DR

This paper introduces a multilevel DFT response theory framework that combines quantum and molecular mechanics layers to accurately compute molecular response properties in complex environments, validated by experiments.

Contribution

The work extends multilevel DFT to response properties and integrates a polarizable MM layer, enabling efficient and accurate response calculations in solvated systems.

Findings

Accurately computed polarizabilities and hyperpolarizabilities of PNA and HBA.

Framework matches experimental results, confirming reliability.

Provides insights into solute-solvent interactions through response property analysis.

Abstract

We present a general computational protocol for the evaluation of extensive molecular response properties in complex environments within a polarizable quantum embedding framework. The approach extends multilevel density functional theory (MLDFT) to response theory by formulating the coupled-perturbed Kohn-Sham (CPKS) equations for the MLDFT Hamiltonian. The method is further coupled to an additional polarizable molecular mechanics layer based on the fluctuating-charge (FQ) force field, which allows an accurate yet computationally efficient description of long-range interactions. We apply this new protocol to compute static and frequency-dependent linear polarizabilities and first hyperpolarizabilities of para-nitroaniline (PNA) in 1,4-dioxane and 3-hydroxybenzoic acid (HBA) in aqueous solution. The framework enables physicochemical insight into solute-solvent interactions by disentangling the competing roles of electrostatics, mutual polarization, and quantum confinement (Pauli repulsion). The results match available experiments, demonstrating the reliability and robustness of the proposed approach and providing a viable route for response properties within quantum embedding methods.