The MFCC scheme has been devised to provide a simple approach for approximating the total energies and electron densities of proteins and to calculate approximate protein-ligand interaction energies . In its simplest form, the protein is separated into single amino acids by placing cuts across the peptide bonds. The unsaturated bonds are then capped by acetyl (ACE) and N -methylamide groups (NME) (see Fig. . Disulfide bridges are also cut and capped by methyl sulfide groups.