Monte Carlo evaluation of the equilibrium isotope effects using the Takahashi-Imada factorization of the Feynman path integral

摘要

The Feynman path integral approach for computing equilibrium isotope effectsand isotope fractionation corrects the approximations made in standard methods,although at significantly increased computational cost. We describe anaccelerated path integral approach based on three ingredients: the fourth-order Takahashi-Imada factorization of the path integral, thermodynamicintegration with respect to mass, and centroid virial estimators for relevantfree energy derivatives. While the frst ingredient speeds up convergence to thequantum limit, the second and third improve statistical convergence. Thecombined method is applied to compute the equilibrium constants for isotopeexchange reactions H2+D=H+HD and H2+D2=2HD.