Enhanced replica exchange reactive Monte Carlo simulations for constructing zeolite frameworks

Abstract

We investigate the ability of a reactive model of silica to build crystalline zeolite frameworks with an enhanced sampling approach based on replica exchange Monte Carlo (REMC) simulations. In our implementation of REMC, the silica hydrolysis/condensation equilibrium constant controlling network formation is chosen as the index parameter characterising each replica. We show that improving the performance of the REMC method by increasing its efficiency in producing zeolite crystals allows zeolites with larger unit cells to be constructed. In particular, we perform an efficiency case study on the sodalite structure, containing 12 tetrahedra per unit cell and then apply the resulting enhancements to construct a significantly larger zeolite. We have improved our simulations in two ways; first, we have analysed the roles of the Monte Carlo parameters on the efficiency of this REMC method. Second, we have implemented an adaptive protocol that resets the values of the hydrolysis/condensation equilibrium constants among the replicas, ‘on the fly’ of each simulation, to optimise replica exchange for the purpose of constructing zeolite crystals. Finally, we show that by applying these enhancements, the REMC method can produce the crystal structure of zeolite AWW, a nanoporous material with 24 tetrahedra per unit cell.