where Scontact, Voverlap, and Eelec
are contact surface, overlapped
volume, and electrostatic interaction energy between
the rotamer and other parts of the protein, respectively; f is
the observed frequency of the rotamer given a backbone
conformation; and Nphil is the number of totally buried
nonhydrogen-bonded hydrophilic atoms at the interface. The
values in the equation are optimized weights of the
energy terms (the weight for Scontact was set to −1).