2.4. Analysis of electrostatic complementarity using the pESP
By comparison between the pESPs of proteins A and B at the PPI interface, the electrostatic complementarity of the two proteins in the complex condition can be analyzed. The most important point of this analysis is that a fully quantum mechanical EDN and ESP are used, by which the effect of charge transfer or polarization due to complex formation is fairly considered. Generally, quantum chemical calculations of the EDN and ESP of a large molecule like a protein are difficult because too much computational effort is required. By using the FMO method, however, the computational effort can be greatly reduced.