Comparison of density functional theory and molecular simulation methods for pore size distribution of mesoporous materials

Abstract

The pore size distribution (PSD) is the major characteristics of the heterogeneity for the mesoporous materials. Together with statistics integral equation, two methods, grand canonical Monte Carlo (GCMC) method and density functional theory (DFT), are used to study the PSD of mesoporous materials. In order to compare the two methods, the PSD of activated meso-carbon microbeads (a-MCMBs) is calculated based on the nitrogen adsorption isotherm at 77 K. In GCMC simulation and DFT calculation, the nitrogen is modeled as a Lennord-Jones (LJ) spherical molecule. The well-known steele's 10-4-3 potential is used to represent the interaction between the fluid molecule and the solid wall. The weighted density approximation of Tarazona's theory is used to get the free energy. The PSDs for the mesoporous material predicted by the two methods are in good line for larger pore sizes (larger than 1.125 nm), while for small pore sizes, DFT deviates significantly due to inherent approximations.