GGA functions by incorporating the gradient of the electron density into the functional form of the exchange-correlation energy. This is mathematically represented as: Exc [Ï] = â« f(Ï(r), âÏ(r)) d3r Where Exc is the exchange-correlation energy, Ï(r) is the electron density, and âÏ(r) is the gradient of the electron density. The functional form f(Ï(r), âÏ(r)) varies depending on the specific GGA functional being used, such as PBE, PW91, or BLYP.
