THE EFFECT OF ANHARMONICITY ON THE SPECTRAL SHAPE OF LINEAR-CHAINS

The spectral shape of a non-linear Lennard-Jones chain is studied usin g various orders of perturbation theory. We include self-consistent ph onon and bubble diagram effects and emphasize the importance of the su m rule. The double-peaked structure that we find in our spectral distr ibutions, which survives the higher-order corrections included in this paper, is discussed. We make a comparison of our results with those o btained using molecular dynamics and the Zwanzig-Mori continued-fracti on (moments) method.