Electrostatic parameters of ionic crystals

More than 200 Madelung constants (MCs), site potentials, and electric field gradient components for ionic crystals of different nature calculated by m eans of the modified Madelung-Born method are presented. The same technique has helped in finding superposition rules interconnecting different classi c crystals, which are useful for checking the accuracy of calculated MCs, t he local site potentials, and electric field gradient tensors. The definiti on of Madelung interaction potentials (MIPs) is introduced, and these purel y geometric quantities, independent of particular charge distribution, are found the most suitable for tabulation of crystal electric field parameters . MIPs are calculated between a number of characteristic points of fee, bcc , hcp, and some other cells. MIPs depend strongly on the choice of cell geo metric parameters but allow easy calculation of the local potentials for ar bitrary point charge distribution, which are independent of this choice. Th e site potentials determined for yttrium ceramics, fullerides, and superful lerides make it possible to examine some regularities useful for interpreta tion of the observed phenomena already at the electrostatic level. The comp arison of the most recent results with the calculations of MC of known crys tals by means of the Evald and other techniques reveals complete agreement. The advantages of the present approach are manifested in calculations of t he surface electrostatic parameters, which are found for a number of crysta l planes, surfaces, and sets of layers including those composed of differen t crystals and those containing charged crystal planes. This technique can be applied for computation of MCs, site potentials, and electric field grad ients for a crystal body restricted by two parallel planes, oriented arbitr arily to the crystal axes, in a layer situated at any depth from the surfac e. (C) 2001 American Institute of Physics.