Mean-square displacement of an atom in an anharmonic crystal to O(&#955;<SUP>4</SUP>)

General expressions for all anharmonic contributions of O(&#955;4) to the mean-square displacement of an atom in a crystal have been obtained. Numerical estimates have been made for a nearest-neighbor central-force model of a fcc lattice in the high-temperature limit and in the leading-term approximation. Our estimates for Lennard-Jones systems show that anharmonic contributions of O(&#955;4) cannot be ignored. Estimated recoilless fraction of 9.4-keV transition of 83Kr in solid krypton is found to be quite close to experimental values