INCARs

INCAR is the input parameter file used by the VASP (Vienna Ab initio Simulation Package) to control a calculation. The file is placed in the working directory alongside POSCAR, POTCAR, and KPOINTS. It enumerates electronic, ionic, and output options as a set of parameter names and values. VASP reads INCAR at startup and uses the specified values to configure the run, convergence criteria, and data generation.

The format is plain text. Each line typically contains a parameter name and a value, using an equals sign or a space-separated form. The official VASP manual lists the supported keywords and valid value ranges. Users often maintain separate INCAR files for different steps of a calculation or different materials in a workflow.

Commonly used parameters (examples):

- ENCUT: plane-wave energy cutoff.

- PREC: precision level (Normal, Accurate, High).

- ISMEAR and SIGMA: smearing method and width for metallic systems.

- EDIFF: electronic convergence criterion.

- NSW and IBRION: ionic relaxation controls; NSW is the maximum number of ionic steps, IBRION selects the relaxation algorithm.

- ISIF: controls relaxation of cell shape, volume, and ions.

- ISPIN and MAGMOM: spin polarization and initial magnetic moments.

- LCHARG and LWAVE: write CHGCAR and WAVECAR files.

- LORBIT: orbital-resolved density of states projections.

INCARs can be tailored for different calculation stages. In workflows or high-throughput studies, multiple INCAR files (for example INCAR.relax, INCAR.static, INCAR.spinorbit) may be used to manage distinct steps, with scripts selecting the appropriate file for each run.