Path integral computation of quantum free energy differences due to alchemical transformations involving mass and potential.

Journal Of Chemical Theory And Computation 7, 2358 - 2369 (2011)

Path integral computation of quantum free energy differences due to alchemical transformations involving mass and potential.

Alejandro Perez, O. Anatole von Lilienfeld.

Thermodynamic integration, perturbation theory, and lambda-dynamics methods were applied to path integral molecular dynamics calculations to investigate free energy di fferences due to alchemical transformations. Several estimators were formulated to compute free energy di erences in solvable model systems undergoing changes in mass and/or potential. Linear and non-linear alchemical interpolations were simulated for the thermodynamic integration. We fi nd improved convergence for the virial estimators, as well as for the thermodynamic integration over nonlinear interpolation paths. Numerical results for the perturbative treatment of changes in mass and electric field strength in model systems are presented. We used thermodynamic integration and ab initio path integral molecular dynamics to compute the free energy di erence of the isotope transformation in the Zundel cation. The performance of di fferent free energy methods is discussed.