TEMPERATURE-DEPENDENT SPECTRAL DENSITIES AND QUANTUM ACTIVATED RATE THEORY

The variability with temperature of spectral densities and rates calcu lated with quantum activated rate theory is investigated. Classical sp ectral densities at two temperatures are computed via molecular dynami cs for a model of proton transfer in methyl chloride. In addition, qua ntum dynamics is computed for spectral densities which artificially bo ost variability at low frequency. We find significant variation in com puted spectral densities at moderate frequency. These variations, howe ver, have little effect on overall computed quantum dynamics. In contr adistinction, artificial variation in spectral densities at the lowest frequencies can generate fairly significant effects on quantum dynami cs. Detailed flux correlation function calculations are presented whic h illustrate this phenomenon. (C) 1998 American Institute of Physics. [S0021-9606(98)51237-8].