Multicomponent Heat-Bath Configuration Interaction with the Perturbative Correction for the Calculation of Protonic Excited States

TL;DR

This paper extends the multicomponent heat-bath configuration interaction (HCI) method to excited states by implementing a perturbative correction and introduces a new approach for calculating reference excitation energies, improving accuracy in protonic excited state calculations.

Contribution

The study introduces a second-order perturbative correction to multicomponent HCI and a novel FGH-based method for reference excitation energies, enhancing excited-state calculations.

Findings

Achieves similar accuracy to existing methods like TDDFT and EOM-CC for protonic excitations.

Demonstrates the effectiveness of the perturbative correction in excited-state energy calculations.

Provides a new approach to isolate basis set errors in multicomponent methods.

Abstract

In this study, we extend the multicomponent heat-bath configuration interaction (HCI) method to excited states. Previous multicomponent HCI studies have been performed using only the variational stage of the HCI algorithm as they have largely focused on the calculation of protonic densities. Because this study focuses on energetic quantities, a second-order perturbative correction after the variational stage is essential. Therefore, this study implements the second-order Epstein-Nesbet correction to the variational stage of multicomponent HCI for the first time. Additionally, this study introduces a new procedure for calculating reference excitation energies for multicomponent methods using the Fourier-grid Hamiltonian (FGH) method, which should allow the one-particle electronic basis set errors to be better isolated from errors arising from an incomplete description of electron-proton correlation. The excited-state multicomponent HCI method is benchmarked by computing protonic excitations of the HCN and FHF-molecules and is shown to be of similar accuracy to previous excited-state multicomponent methods such as multicomponent time-dependent density functional theory and equation-of-motion coupled-cluster theory relative to the new FGH reference values.