Quantum reaction rate from higher derivatives of the thermal flux-flux autocorrelation function at time zero.

A quantum theory of thermal reaction rates is presented which maybe viewed as an extension of the recently developed "quantum instanton" (QI) model [W. H. Miller, Y. Zhao, M. Ceotto, and S. Yang, J. Chem. Phys. 119, 1329 (2003)]. It is based on using higher derivatives of the flux-flux autocorrelation function C(t) (as given by Miller, Schwartz, and Tromp) at t=0 to construct a short time approximation for C(t). Tests of this theory on 1 d and collinear reactions, both symmetric and asymmetric, show it to be more accurate than the original QI model, giving rate constants to similar to5% for a wide range of temperature. (C) 2005 American Institute of Physics.