I want to calculate binding energy of a protein-ligand or a  protein-protein complex by MMPBSA method after MD simulation run. I uses  DS3.5. I have modelled a protein of 200 Aa long and docked with a  ligand to the active site of this protein molecule by using LibDock  protocol. After docking procedure, select lowest binding energy  conformation (by using calculate binding protocol) for further analysis.  Refined the protein-inhibitor complex with explicit periodic boundary  condition with 10ns MD simulation run. Sampling time is 20ps. Now I want  to calculatethe binding energy of -