Themis: A Software to Assess Association Free Energies via Direct Estimative of Partition Functions

We present the program Themis - a computer implementation of a standard statistical mechanics framework to compute free energies, average energies and entropic contributions for association processes of two atom-based structures. The partition functions are computed analytically using a discrete grid in the phase space, whose size and degree of coarseness can be controlled to allow efficient calculations and to achieve the desired level of accuracy. With this strategy, applications ranging from molecular recognition, chiral discrimination, surface adsorption and even the interactions involving molecules in electronic excited states can be handled.