A computer-implemented method for calculating a value representative of interaction (VRI) of a proposed ligand with a specified receptor. Hydrophobic interactions between one or more ligand atoms and one or more receptor atoms are scored by a method that awards a bonus for the presence of hydrophobic enclosure of one or more ligand atoms by the receptor. Also, charge-charge hydrogen bonds between a ligand and a receptor are scored by setting a default value for a charge-charge hydrogen bond and awarding a bonus above the default value when one or more specialized predetermined charge-charge hydrogen bond criteria is satisfied. Various charge-charge hydrogen bond criteria are used. Zwitterions, charge, salvation, geometry and electrostatic energy are accounted for.