XE-129 ADSORBED IN ALPO4-11 MOLECULAR-SIEVE - MOLECULAR-DYNAMICS SIMULATION OF ADSORBATE DYNAMICS AND NMR CHEMICAL-SHIFT

Molecular dynamics simulation of Xe-129 adsorbed in the AIPO(4)-11 mol ecular sieve has been carried out in the constant NVT ensemble at T = 300 K. The host material was modelled as a fully dynamic framework. Si ngle-particle and pair distribution functions of the adsorbed gas in t he unidirectional channels of the material with different adsorbate lo adings are presented. Self-diffusion coefficients, D-Xe, have been cal culated for the dynamics of the adsorbates between the adsorption cell s in AIPO(4)-11. The dynamic framework is shown to decrease the effect ive potential barrier for intercellular jumps. An estimate is given fo r the jump frequency. The NMR chemical shifts of Xe-129 were evaluated using parametrizations based on first principles calculations of Xe-X e and Xe-OH2 model systems. No adjustable parameters were used to impr ove agreement with experimental results. The results of a phenomenolog ical three-site dynamic averaging model proposed earlier by others wer e reproduced with a good accuracy using chemical shift parameters from gradient corrected density-functional theory. Finally, the approximat ions inherent to the present computational approach are discussed. (C) 1997 American Institute of Physics.