Exchange-Correlation Functional

The Exchange-Correlation (XC) functional is the heart of DFT, approximating the complex many-body electron interactions. The choice of functional determines the fundamental accuracy of the simulation.

• Functional: Selects the family, or "rung" on Jacob's Ladder of DFT. 'LDA' (Local Density Approximation) is the simplest. 'GGA' (Generalized Gradient Approximation) is a standard choice for many solids. 'VDW' includes non-local corrections for van der Waals interactions.
• Authors: Selects the specific parameterization within a functional family (e.g., 'PBE' or 'PBEsol' within GGA). The choice can significantly affect results like lattice constants and bond energies.