FIG. 2.

(a) The derivative (∂ΔG_rep/∂x_i) of the repulsive (ΔG_rep) component of the van der Waals component (ΔG_vdw) of the solvation free energy with respect to the coordinates (x_i) of the atomic centers as a function of the derivative (∂A/∂x_i) of the solvent-accessible surface area (A) with respect to the x_i. (b) The probability densities (f) of the angle (θ) between ∇_iA and ∇_iΔG_rep where ∇_i = (∂/∂x_i, ∂/∂y_i, ∂/∂z_i) and (x_i, y_i, z_i) were the coordinates of the center of atom i. The points in (a) and the curves in (b) are colored by the atom type in the CHARMM27 force field. The values in (a) and (b) were computed with the CHARMM27 force field and configurations taken from a simulation run with CHARMM27. (c) and (d) The same as (a) and (b), respectively, but the values in these plots were computed with AMBER ff12sb and configurations taken from a simulation run with AMBER ff12sb.