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

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, D_Xe, 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 Xe 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.