INTERATOMIC CORRELATION MOMENTS AND MEAN-SQUARE RELATIVE DISPLACEMENTS IN AN ANHARMONIC CRYSTAL WITH THE FACE-CENTERED-CUBIC LATTICE

Using the correlative method of unsymmetrized self-consistent field we study the dynamical properties of anharmonic crystals, namely, the qu adratic correlations between atomic displacements from the equilibrium positions and their mean square relative displacements in anharmonic crystals. In the present paper we calculate these values for a weakly anharmonic crystals with the face-centered cubic lattice in which the nearest neighbors interact. The second order of the method enables one to calculate for this lattice the correlations between the nearest, s econd, third and fourth neighbors. The results are compared with those obtained previously for simplified models. The dependence on the coor dination number and on the dimensionality of the lattice is discussed.