(660g) Determining Absolute Free Energy of Heterogeneous Molecular Solids

The Einstein crystal method proposed by Frenkel and Ladd in 1984 has become a standard method for absolute free energy calculations. In the last two decades, this method was widely applied to homogenous systems, for example, hard-sphere solids, hard-ellipsoid systems, Lennard-Jones solids and solid phases of water.  We extended the Einstein crystal method to heterogeneous solid systems, specifically, nano-confined systems in which a fluid, that would be in the liquid state in the bulk, is nanoconfined between slit pores of another solid.  In this work, we use free energy calculations to quantitatively explore the fundamental issues associated with nano-confined phenomena, such as, the effect of fluid-wall interaction and the influence of wall-wall separation on confined phase. Moreover, with the goal to resolve the long standing controversy among experiments and simulations -- whether sufficient nano-confinement by molecularly smooth mica sheets will induce a phase change of organic fluid -- we compare the absolute Helmholtz free energy of the nano-confined solid and its corresponding nano-confined fluid state to conclusively determine the stable state of simple nano-confined systems.