A general method for computing kinetic isotope effects is described. The
method uses the quantum-instanton approximation and is based on the
thermodynamic integration with respect to the mass of the isotopes and on the
path-integral Monte-Carlo evaluation of relevant thermodynamic quantities. The
central ingredients of the method are the Monte-Carlo estimators for the
logarithmic derivatives of the partition function and the delta-delta
correlation function. Several alternative estimators for these quantities are
described here and their merits are compared on the benchmark hydrogen-exchange
reaction, H+H_2->H_2+H on the Truhlar-Kuppermann potential energy surface.
Finally, a qualitative discussion of issues arising in many-dimensional systems
is provided.Comment: 11 pages, 2 figures, proceeding