PROCAR

PROCAR is a data file associated with the Vienna Ab initio Simulation Package (VASP) used to analyze the orbital character of electronic states in periodic systems. It provides projections of Kohn–Sham wavefunctions onto atomic orbitals, organized by k-point, band index, atom, and angular momentum channel (for example s, p, and d). In spin-polarized calculations, PROCAR can separate contributions from different spin channels, enabling the study of spin-resolved orbital character.

The file contents allow users to see how much each atom and orbital type contributes to a given Bloch state, facilitating interpretation of the band structure. Researchers use PROCAR to identify bonding character, orbital hybridization, and the origins of features in bands and density of states, as well as to analyze changes under structural or chemical modifications.

Generation and usage are tied to VASP’s projection analysis features. PROCAR is produced when orbital projections are requested and appropriate calculation settings are used. The resulting data is typically read with plotting or analysis tools, or processed by scripts to produce orbital-resolved band plots or to quantify contributions from specific atoms or orbitals.

Limitations and interpretation considerations are important. Projections depend on the chosen basis and projection scheme, and different computational methods or software may define the quantities differently. Consequently, PROCAR is most useful for qualitative comparisons and trends rather than as an absolute measure of orbital contributions.

See also: VASP, Kohn–Sham wavefunctions, orbital-projected analysis, electronic structure.