Molecular dynamics simulation studies on ethane and acetylene mixture in CuBTC metal organic framework

Abstract

Molecular Dynamics (MD) simulation studies have been carried out on the mixture containing ethane and acetylene molecules in 1:1 ratio at various concentrations of each species in CuBTC metal organic framework (MOF). MOFs are important class of materials which are tremendously useful for applications such as gas storage and separation. They have complex structure consisting of pore and pockets connected by windows. Results obtained from MD simulation showed that the self diffusivity of the ethane increases with the concentration while it decreases in case of acetylene. Correlation effects are responsible for this kind of phenomena. Pair distribution function showed the strong peaks at higher correlation length indicating the complex crystalline structure of the host matrix. We have also obtained the velocity auto correlation function (VACF) and velocity cross correlation functions (VCCF) at each studied concentration and found that the contribution from VCCF is almost negligible at lower concentration. Since the transport properties of mixture also depend on the mutual diffusivity and distinct diffusivity besides the self diffusivity, attempt has been made to quantify both the diffusivities. In the present system, at lower concentration, contribution to the mutual diffusivity comes from self diffusivities of species alone and distinct diffusivity contributes only at higher concentration.