Xe 129 adsorbed in AlPO4-11 molecular sieve: Molecular dynamics simulation of adsorbate dynamics and NMR chemical shift

Abstract

Molecular dynamics simulation of 129Xe adsorbed in the AlPO4-11 molecular sieve has been carried out in the constant NVT ensemble at T=300 K. The host material was modeled as a fully dynamic framework. Single-particle and pair distribution functions of the adsorbed gas in the unidirectional channels of the material with different adsorbate loadings are presented. Self-diffusion coefficients, DXe, have been calculated for the dynamics of the adsorbates between the adsorption cells in AlPO4-11. The dynamic framework is shown to decrease the effective potential barrier for intercellular jumps. An estimate is given for the jump frequency. The NMR chemical shifts of 129Xe were evaluated using parametrizations based on first principles calculations of Xe–Xe and Xe-OH2 model systems. No adjustable parameters were used to improve agreement with experimental results. The results of a phenomenological three-site dynamic averaging model proposed earlier by others were reproduced with a good accuracy using chemical shift parameters from gradient corrected density-functional theory. Finally, the approximations inherent to the present computational approach are discussed.