Hi Navnit, I don't have any further advice. Entropy is a statistical property regarding the number of available conformations, quantum states or classically the accessible volume of phase space (position and momentum coordinates of ligand, receptor, solvent and ions). I imagine you can get some estimate from an MD trajectory. Comparing the "vdw volume" versus the volume of a solvent excluded surface says something about the entropy effects due to solvent exclusion. The difference in volumes is just from the nooks where the water molecules can't reach. But it doesn't include entropy from motion confinement of ligand and receptor. As mentioned before the closest you'll get to the vdw volume in the current Chimera is a solvent excluded surface with small probe radius (0.5A minimum allowed, default is 1.4A). Tom