Ab initio calculations of NMR chemical shieldings for the ionic and the superionic AgI

The chemical shift calculations for AgI crystal in the ionic and superionic phases are performed from the point of view of the average shielding value. The average shielding values are given by the sum of convolutions of a probability density and a shielding surface of Ag atom. The probability density involves effects of the diffusion and the vibration depending on the temperature. The shielding surface is estimated by the ab initio MO calculation by using model molecules. The calculated temperature dependences of the chemical shift were in good agreement with the observed one. In both the phases, it was clear that the broadening of the cation density due to the diffusive and vibrational motions resulted in the NMR high field shift. (C) 2002 Elsevier Science B.V. All rights reserved.