The gCP (Geometrical Counter-Poise) correction method is a way to deal
with the basis set superposition error (BSSE) in quantum chemical
calculations.

The BSSE is a fundamental error that occurs in all practical electronic
structure calculations that use finite basis sets. The gCP is a
semi-empirical method that is much more efficient than the standard
Boys-Bernardi counterpoise (BB-CP) correction, especially for geometry
optimizations.