CPMD/GULP QM/MM Interface for Modeling Periodic Solids: Implementation and its Application in the Study of Y-Zeolite Supported Rh$_n$ Clusters

TL;DR

This paper presents a new hybrid QM/MM interface combining CPMD and GULP for modeling periodic solids, enabling efficient and accurate simulations of complex systems like zeolite-supported metal clusters.

Contribution

The authors developed and validated a parallelized QM/MM interface between CPMD and GULP, allowing full relaxation and dynamics of large periodic systems with electrostatic coupling.

Findings

Validated for energy conservation and scalability.

Studied oxygen vacancy in cristobalite with good agreement.

Analyzed Rh cluster structures in Y-zeolite.

Abstract

We report here the development of hybrid quantum mechanics/molecular mechanics (QM/MM) interface between the plane-wave density functional theory based CPMD code and the empirical force-field based GULP code for modeling periodic solids and surfaces. The hybrid QM/MM interface is based on the electrostatic coupling between QM and MM regions. The interface is designed for carrying out full relaxation of all the QM and MM atoms during geometry optimizations and molecular dynamics simulations, including the boundary atoms. Both Born-Oppenheimer and Car-Parrinello molecular dynamics schemes are enabled for the QM part during the QM/MM calculations. This interface has the advantage of parallelization of both the programs such that the QM and MM force evaluations can be carried out in parallel in order to model large systems. The interface program is first validated for total energy conservation and parallel scaling performance is benchmarked. Oxygen vacancy in {\alpha}-cristobalite is then studied in detail and the results are compared with a fully QM calculation and experimental data. Subsequently, we use our implementation to investigate the structure of rhodium cluster (Rh$_n$ ; $n$=2 to 6) formed from Rh(C$_2$H$_4$)$_2$ complex adsorbed within a cavity of Y-zeolite in a reducible atmosphere of H$_2$ gas.