The invention provides a computer implemented method of quantifying the quality of packing for a residue comprising one or more residue atoms in a first protein in a first conformation, the method comprising: (a) calculating one or more close contact potentials based on a distance between the one or more residue atoms and one or more environment atoms, (b) calculating a contact area of the one or more residue atoms that is exposed to the one or more environment atoms and (c) calculating a close contact surface density (CCSD) by dividing the sum of the one or more close contact potentials by the contact area.