Protein Data Bank force field calculations

Figure 2 Energy in kcal mol vs. phi, psi values based on a survey of the Brookhaven Protein Data Bank and from the CHARMM22 empirical force field. The protein survey data was placed into 15° x 15° bins and converted to free energies based on a Boltzmann distribution. The CHARMM22 surface was obtained by optimizing all degrees of freedom except for the phi and psi dihedrals at 15° increments. Note the CHARMM22 ALAD surface should not be considered to be rigorously correct however, the number and location of the minima are consistent with ab initio calculations ...

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