Multidimensional direct free energy perturbation.

In this work we propose a multidimensional free energy perturbation scheme that allows the evaluation of the free energy difference between a state sampled based on importance sampling and almost any state that can be constructed by the reduction of the number of molecules in the system and the change of either the interaction energy or the thermodynamic state variable (e.g., the temperature) of the system. We show that via this approach it is possible to evaluate any thermodynamic property included but not limited to free energy, chemical potential, and pressure, along a series of isotherms from a single molecular simulation.