T. Keyes et Jt. Fourkas, Instantaneous normal mode theory of more complicated correlation functions: Third- and fifth-order optical response, J CHEM PHYS, 112(1), 2000, pp. 287-293
A general procedure is given for calculation of time correlations in liquid
s, including complex multitime functions, with instantaneous normal modes (
INM). The method requires equilibrium averages only and eliminates any need
to invoke a fictitious harmonic well. The third and fifth order optical re
sponse functions, and the self- and collective-density correlations, are ob
tained and compared with the results of other methods. INM provides several
advantages for evaluating the nonlinear response function required for fif
th-order scattering. The time expansions of the response functions, and the
role of anharmonicity, are discussed. (C) 2000 American Institute of Physi
cs. [S0021-9606(99)51646-2].