2.5. Implementation
In this study, the pEDN (equations (2) and (3)) and pESP (equations (6)
and (7)) were implemented in PAICS,39 which is our
original FMO program package. In PAICS, EDN and ESP at the MP2 level of
theory can be efficiently calculated by using RI
approximation.24 In the current implementation, the
grid data of the pEDN and pESP of proteins A and B are transferred to
separate files, and the differential EDN is obtained by simply
subtracting the pEDNs and used to define the PPI interface. To analyze
the electrostatic complementarity of the PPI, the pESPs of proteins A
and B are visualized at the PPI interface. Here, such a visualization of
the grid data was performed with UCSF Chimera.40