incar

INCAR is the primary input file for VASP (the Vienna Ab initio Simulation Package) that specifies run-time parameters for a density functional theory calculation. It is a plain text file containing keyword=value pairs that control electronic structure, ionic relaxation, and various operational settings. The file works alongside POSCAR (structure), POTCAR (pseudopotentials), and KPOINTS (Brillouin zone sampling). The tags in INCAR override VASP defaults, and missing tags use preset defaults.

Structure and usage: Each line typically contains a keyword and a value. Comments can be added with a leading #. VASP reads INCAR at startup and applies the settings to the entire calculation; different INCARs can be used for successive steps in a workflow.

Common categories and example tags: Electronic convergence and accuracy include ENCUT (plane-wave cutoff energy), ISMEAR and SIGMA (smearing method and width), EDIFF (electronic energy convergence criterion). Ionic relaxation and optimization include NSW (maximum ionic steps), IBRION (ionic relaxation algorithm), ISIF (controls relaxation of ions and cell shape). Spin and magnetism involve ISPIN (spin polarization) and MAGMOM (initial magnetic moments). Output control includes LCHARG and LWAVE (write charges and wavefunctions), LREAL (real-space projection for efficiency), and LORBIT (PDOS projections).

Other notes: The specific set of INCAR tags varies with calculation type (static, geometry optimization, molecular dynamics) and with the chosen pseudopotentials. The INCAR is located in the calculation directory and, together with POSCAR, POTCAR, and KPOINTS, defines the computation. Changes to INCAR typically require restarting or carefully managing convergence.