The Molecular Mechanics Poisson-Boltzmann Surface Area (MMPBSA) approach has been widely applied as an efficient and reliable free energy simulation method to model molecular recognition, such as for protein-ligand binding interactions. MM/PBSA is a popular method to calculate absolute binding affinities with a modest computational effort. tl;dr: MMPBSA uses the Poisson-Boltzmann equation to compute the electrostatic contribution to the free-energy; MMGBSA uses the Generalized Born. In the MM-PBSA approach the different contributions to the binding free energy above are calculated in various ways: Solvation free energies are calculated by. In the past decade, MM/GBSA and MM/PBSA may be the most popular methods for large-scale binding free energy calculations due to their acceptable accuracy,. MM/PBSA is simply a post-processing technique whereby the free energy of a state is calculated from the internal energy (MM) of the molecule.