Surface adsorption at the thermodynamic limit using periodic DLPNO-MP2 theory: A study of CO on MgO at dilute and dense coverages

TL;DR

This study uses periodic DLPNO-MP2 theory to accurately model CO adsorption on MgO surfaces across different coverages, revealing coverage-dependent binding energies and demonstrating the method's efficiency for large, complex surface systems.

Contribution

The paper introduces the application of periodic DLPNO-MP2 to study surface adsorption at the thermodynamic limit, enabling simulations of dense coverages beyond single unit cells.

Findings

Adsorption energies agree with benchmarks in dilute regimes.

Binding strength decreases at full monolayer coverage.

Lateral repulsions explain coverage-dependent adsorption energy changes.

Abstract

We apply periodic domain-based local pair natural orbital second-order M{\o}ller--Plesset perturbation theory (DLPNO-MP2) to probe the adsorption energy of CO on MgO(001), the consensus toy model system for surface adsorption. A number of robust correlated wavefunction methods now achieve excellent agreement with experiment for the adsorption of a single CO molecule onto the MgO surface. However, studies probing denser coverage ratios are scarce because of the increased computational expense and the larger configuration space to optimize. We leverage the computational efficiency of periodic DLPNO-MP2 to perform simulations beyond a single unit cell. By using large supercells, we highlight the importance of accurately representing the thermodynamic limit of the surface, and demonstrate in turn that different coverage ratios can be consistently probed. In the dilute regime, we show that adsorption energies obtained from periodic DLPNO-MP2 agree with existing benchmarks. We then obtain adsorption energies at increasing densities approaching full monolayer coverage. Our results show a reduction in binding strength at full coverage, agreeing with experimental observations, which is explained by the increasing lateral repulsions between the COs. This study demonstrates the efficacy of periodic DLPNO-MP2 for probing increasingly sophisticated adsorption systems at the thermodynamic limit.