The Lazaridis-Karplus solvation energy (fa_sol) scores the energy of a molecule in implicit solvent using a Gaussian-exclusion solvent model. The term was originally described in this paper. Rosetta uses this model with a few adjustments:
The desolvation energy function has the exponential form described in Equations 5–7 only for a certain range of interatomic distances. For other distances Rosetta uses approximating forms (see "Etable::analytic_lk_evaluation()").
By default the contributions of some atom pairs are ignored (e.g., the intra-residue contributions and the contributions ignored via the count-pair mechanism).
The DELTA_G_REF constant energy offsets are ignored. This value is conceptually folded into the grab-bag of residue-type-constant energies that is the reference energy.
The unweighted solvation energies are expressed in kcal/mol.