POTCAR

POTCAR is a pseudopotential file used by the Vienna Ab initio Simulation Package (VASP) to describe the interaction between ions and electrons within density functional theory calculations that employ the projector augmented-wave (PAW) method. It serves as the reference data set for the atomic species present in a simulation.

The file typically contains concatenated data blocks for one or more chemical elements. Each block encodes the PAW potential for a single element, including information about core and valence states, projector functions, and other parameters that define the potential. The blocks are arranged in the same order as the atomic species listed in the simulation and, for a given calculation, the order of POTCAR blocks should match the order of atoms in the POSCAR file.

POTCARs are distributed from official libraries and repositories associated with VASP or compatible third-party sources. The content of a POTCAR block depends on the chosen exchange-correlation functional (for example, PBE or LDA) and on the specific potential family (PAW in VASP, with variations in core treatment and radii). As a result, different POTCARs for the same element can exist.

To assemble a POTCAR, users typically obtain the individual elemental POTCARs from a library and concatenate them in the required order. It is important to ensure consistency of functional and potential family across all elements to avoid calculation errors. POTCAR files are distinct from the POSCAR, INCAR, and KPOINTS inputs and are central to the accuracy and convergence of VASP simulations.