Efficient Monte Carlo Simulations of Gas Molecules Inside Porous Materials

Abstract

Monte Carlo (MC) simulations are commonly used to obtain adsorption properties of gas molecules inside porous materials. In this work, we discuss various optimization strategies that lead to faster MC simulations with CO 2 gas molecules inside host zeolite structures used as a test system. The reciprocal space contribution of the gas−gas Ewald summation and both the direct and the reciprocal gas−host potential energy interactions are stored inside energy grids to reduce the wall time in the MC simulations. Additional speedup can be obtained by selectively calling the routine that computes the gas−gas Ewald summation, which does not impact the accuracy of the zeolite's adsorption characteristics. We utilize two-level densitybiased sampling technique in the grand canonical Monte Carlo (GCMC) algorithm to restrict CO 2 insertion moves into lowenergy regions within the zeolite materials to accelerate convergence. Finally, we make use of the graphics processing units (GPUs) hardware to conduct multiple MC simulations in parallel via judiciously mapping the GPU threads to available workload. As a result, we can obtain a CO 2 adsorption isotherm curve with 14 pressure values (up to 10 atm) for a zeolite structure within a minute of total compute wall time.

New materials for methane capture from dilute and medium-concentration sources

“…Cutting-edge computational tools were employed, including a DFT-based quantum-chemical implicit solvent formalism 13 for the liquid solvents and a recently developed, highly efficient sorption code 26,27 for the zeolites that employs classical force fields with well-validated parameter sets. Two specific application areas were targeted, that is, concentrating methane from a medium-concentration source to a high concentration (for example, purifying a low-quality natural gas) and concentrating a very dilute methane stream into one of the moderate concentrations (for example, enabling energy production from coal-mine ventilation air).…”

“…The Henry's constant and the pure component adsorption isotherms for CO 2 , CH 4 and N 2 gas molecules were computed using our highly efficient graphics processing unit code 26,27 , and the Ideal Adsorbed Solution Theory was then applied to estimate the mixture component uptake to reproduce the aforementioned conditions relevant to methane separations 39 . In our simulations, all interactions between gas molecules and the zeolite framework were described at the classical force field level with atomic partial charges (for Coulombic interactions) and 12-6 Lennard-Jones parameters (for van der Waals interactions) taken from Garcia-Perez et al 40 The framework was assumed to be rigid throughout the simulations, an assumption that is considered to be reasonable in zeolite structures 41 .…”

Large-Scale Screening of Zeolite Structures for CO2 Membrane Separations

“…We have utilized various efficient techniques such as density biased sampling, energy grid usage, and parallelization of energy calculations to reduce the average overall wall time of a single GCMC simulation to under a minute. 35 The number of equilibration cycles and production cycles were set respectively at 250 000 and 100 000. The mixture isotherms were obtained from the computed pure isotherm data using the IAST, which has been demonstrated to be generally applicable to make good predictions about mixture behaviors for various porous materials.…”

Percolation through voids around overlapping spheres: A dynamically based finite-size scaling analysis

“…Systems comprised of randomly placed spheres have been used to provide a microscopically valid description of the structure of catalysts [2][3][4][5][6], and in such * djpriour@ysu.edu recent engineering contexts dynamically based simulations probe the function of catalyst structures. Theoretical studies of transport in zeolites [7,8], though not directly concerned with calculating a percolation threshold, entail characterizing the spaces between ions comprising the zeolite, which are modeled as spheres. Hydrometalation catalysts have been found to be more adequately modeled as being comprised of randomly placed spheres than other geometries such as cylinders and needles [6].…”