# Parameterization in the generalised gradient approximation (GGA)

Disclaimer: Assume the person asking is a novice in DFT and condensed matter physics in general.

In the localized density approximation (LDA), the exchange correlation potential is considered a function of a constant charge density, whereas in GGA, it is a function of the gradient of charge density as well:

$$$$V_{(xc)}^{LDA} = f(\rho_{(r)})$$$$

$$$$V_{(xc)}^{GGA} = f(\rho_{(r)},\nabla\rho_{(r)})$$$$

What role does the constant charge density play in GGA? Also, in literature, methods describe DFT calculations done with GGA as parameterized by so-and-so. What does that mean?