Quantum mechanical thermal rate constants using flux–flux correlation functions and Padé analytical continuation procedures

A new expression for a thermal reaction rate is derived. It is based on the flux–flux correlation function approach and a finite basis set representation but differs from the Miller–Schwartz–Tromp (MST) formulation [J. Chem. Phys. 79, 4889 (1983)] by substitution of time dependent sine functions by parameter dependent Lorentzians. Then we apply Padé extrapolation procedure to eliminate the parameter. This operation replaces the search for stability of the time dependent rate in the MST approach. The convergence of the method is checked on the one dimensional Eckart barrier as an illustrative example.