Active Spaces and Non-Orthogonal Configuration Interaction Approaches for Investigating Molecules on Metal 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 (Γ) limits as well as the strong and weak electron–electron repulsion (U) limits. We obtain accurate results as compared with exact numerical renormalization group theory, recovering charge transfer states where appropriate. The current framework should open a path to run molecular non-adiabatic dynamics on metal surfaces.

Nonadiabatic Potential Energy Surfaces for a Molecule on a Surface as Found by Constrained Complete Active Space Theory

“…With this background in mind, we have sought to explore whether standard (but slightly tweaked) quantum chemistry methods can solve such an interface problem, in particular CASSCF-like solutions. Our recent forays into different versions of Hartree–Fock theory with nonorthogonal orbitals [partially optimized closed or open shell Hartree–Fock (poCOOS-HF) have pointed to CASSCF­(2,2) as the most natural (and improved) starting point. To that end, we will explore four different CASSCF-based approaches for modeling the AH model: Standard complete active space self-consistent-field (CASSCF).…”

Modelling Heterogeneous Catalysis using Quantum Computers: An academic and industry perspective

“…In heterogeneous catalysis, where open-shell systems like transition metals and delocalization of electrons are common, strong correlation effects are often present, necessitating methods that go beyond the single-reference/single-configuration approach. [32][33][34][35] Multireference/multiconfiguration methods, such as complete active space self-consistent field (CASSCF) 36,37 combined with multireference perturbation theory (MRPT), for instance complete active space second-order perturbation theory CASPT2 [38][39][40] or N-electron valence state secondorder perturbation theory (NEVPT2) [41][42][43] are essential to capture static and dynamic correlation and accurately describe the electronic structure and energetics of complex catalytic systems. These advanced methods are crucial for understanding the details of catalytic reaction mechanisms and designing more efficient and selective catalysts for sustainable chemical processes.…”