When using GB/SA solvation, what value should be entered in the “Dielectric constant” field?
The GB/SA continuum solvation model automatically takes into account the dielectric constant of the chosen solvent. When GB/SA is in use, the “Dielectric constant” field represents the “molecular” dielectric constant, as explained in the MacroModel Reference Manual under the opcode FFLD arg5. When modeling proteins, for instance, some modelers set this value up to 4.0, to represent the polar nature of amide polymers. But in general, if GB/SA solvation is being used, a good starting value for this field is 1.0.
