"Configurational Free energy" : Direct free energy calculations in   molecular systems
  In this work, I propose a statistical mechanical framework, for the evaluation of the free energy in molecular systems, by "deleting" all the molecules in a "single" step. The approach can be considered as the statistical mechanics equivalent of the evaluation of the potential energy in classical mechanics by accounting for the necessary work to transfer all molecules one by one to infinite distance. As a result, the free energy of an atomistic system, can now be expressed, as an ensample average over a configurational function that we shall call "configuretional free energy" and correspondent to the contribution of each configurational microstate, to the free energy of the system, provided that the microstates are sampled according to the equilibrium statistics. Moreover, the proposed method is capable of evaluating, the free energy as a function of the density, from the simulated density down to zero. 
Georgios C. Boulougouris
cond-mat.stat-mech cond-mat.mtrl-sci cond-mat.soft physics.chem-ph