Active Spaces and Non-Orthogonal Configuration Interaction Approaches for Investigating Molecules on Metal Surfaces

TL;DR

This paper evaluates multiconfigurational wavefunction methods, including non-orthogonal approaches, for accurately modeling molecules on metal surfaces, demonstrating their effectiveness across different hybridization and electron-electron interaction regimes.

Contribution

It introduces and tests non-orthogonal configuration interaction methods for molecules on metal surfaces, showing improved accuracy over traditional approaches.

Findings

Accurate ground state electron populations obtained compared to NRG.

Effective modeling across strong and weak hybridization regimes.

Potential for non-adiabatic molecular dynamics simulations on surfaces.

Abstract

We test a set of multiconfigurational wavefunction approaches for calculating the ground state electron population for a two-site Anderson model representing a molecule on a metal surface. In particular, we compare (i) a Hartree Fock like wavefunction where frontier orbitals are allowed to be nonorthogonal versus (ii) a fully non-orthogonal configuration interaction wavefunction based on constrained Hartree-Fock states. We test both the strong and weak metal-molecule hybridization ($\Gamma$) limits as well as the strong and weak electron-electron repulsion (U) limits. We obtain accurate results as compared with exact numerical renormalization group (NRG) theory, recovering charge transfer states where appropriate. The current framework should open a path to run molecular non-adiabatic dynamics on metal surfaces.