### Input files

There are four input files necessary to run a VASP job:

- INCAR
- KPOINTS
- POSCAR
- POTCAR

The INCAR file is the central input file. In contains the “what to do” and the “how to do”. Here is an example of an INCAR file:

SYSTEM = Water molecule ISTART = 0 ICHARG = 2 PREC = Normal ENCUT = 400.00 EDIFF = 1E-04 ISMEAR = 2 SIGMA = 0.2 IBRION = 2 NSW = 100 POTIM = 0.2

*ISTART* starts the job. *ISTART=0* means to start a new job from this input file. If you want to use another input file your *ISTART* will have a different value. *ICHARG=2* means take superposition of atomic charge densities. *PREC* defines the precision of the calculation. The default is *Normal*. *ENCUT* is the cut-off for plane wave basis in eV. *EDIFF* is the convergence criteria for the energy. *ISMEAR* determines how the partial occupancies are set for each orbital. The *ISMEAR* value will change depending on the type of system you are interested in. *SIGMA* is the width of smearing. *IBRION* is the amount of relaxation for a system to get the their instantaneous ground state. *NSW* is the maximum number of ionic steps. *POTIM* is the scaling constant for forces in minimization algorithms.

The KPOINTS must contain the k-point coordinates and weights or the mesh size for creating the k-point grid. In VASP 5.2.12 the KPOINTS file may be missing, and the k-point spacing can be supplied in the INCAR file instead. Here is an example of a KPOINTS file:

k-points 0 Gamma 6 6 1 0.5 0.5 0

POSCAR contains the geometry of the atoms and has the lattice vectors to create the periodic structure.

Water molecule 1.0 3.7842 0.0000 0.0000 0.0000 3.7842 0.0000 0.0000 0.0000 50.000 2 1 Cartesian 1.41010 0.00000 0.81704 0.00000 0.02303 0.20953 0.92694 0.05649 0.00000

Note the 2 1 in the input below the lattice vectors. They represent the order of the pseudo potentials in the POTCAR.

POTCAR contains all of the pseudo potential information for the atoms

### Reference

G. Kresse and J. Hafner. Ab initio molecular dynamics for liquid metals. Phys. Rev. B, 47:558, 1993. G. Kresse and J. Hafner. Ab initio molecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium. Phys. Rev. B, 49:14251, 1994. G. Kresse and J. Furthmüller. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mat. Sci., 6:15, 1996. G. Kresse and J. Furthmüller. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B, 54:11169, 1996.

Depending on the potentials used you should also include the following citations:

Ultra-soft pseudopotentials

D. Vanderbilt. Soft self-consistent pseudopotentials in a generalized eigenvalue formalism. Phys. Rev. B, 41:7892, 1990. G. Kresse and J. Hafner. Norm-conserving and ultrasoft pseudopotentials for first-row and transition-elements. J. Phys.: Condens. Matter, 6:8245, 1994.

PAW potentials

P. E. Blochl. Projector augmented-wave method. Phys. Rev. B, 50:17953, 1994. G. Kresse and D. Joubert. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B, 59:1758, 1999.

The references to the exchange and correlation approximations implemented in VASP are:

Local Density Approximation (LDA)

J. P. Perdew and A. Zunger. Self-interaction correction to density-functional approximations for many-electron systems. Phys. Rev. B, 23:5048, 1981.

Generalized Gradient Approximation PW91 (GGA-PW91)

J.P. Perdew, J.A. Chevary, S.H. Vosko, K.A. Jackson, M.R. Pederson, D.J. Singh, and C. Fiolhais. Atoms, molecules, solids, and surfaces: Applications of the generalized gradient approximation for exchange and correlation. Phys. Rev. B, 46:6671, 1992. J.P. Perdew, J.A. Chevary, S.H. Vosko, K.A. Jackson, M.R. Pederson, D.J. Singh, and C. Fiolhais. Erratum: Atoms, molecules, solids, and surfaces: Applications of the generalized gradient approximation for exchange and correlation. Phys. Rev. B, 48:4978, 1993.

Generalized Gradient Approximation PBE (GGA-PBE)

J. P. Perdew, K. Burke, and M. Ernzerhof. Generalized gradient approximation made simple. Phys. Rev. Lett., 77:3865, 1996. J. P. Perdew, K. Burke, and M. Ernzerhof. Erratum: Generalized gradient approximation made simple. Phys. Rev. Lett., 78:1396, 1997.

### More information

Visit the VASP website to download the manual and view VASP workshop lectures.