VASP beginners

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VASP has four input files: INCAR, POSCAR, KPOINTS, and POTCAR. To run VASP in a cluster such as tekla2, [run.sh|you need a fifth file containing the instructions to the queue system]].

To learn to prepare the inputs and understand the outputs, VASP newcomers should become familiar with the documentation and the hands-on included herein. These hands-on were created for VASP 4x, so some flags are outdated. Please generate all input files by yourself rather than blindly running them (or you won't learn the basics). Extend the flags included in the INCAR file to put the ones that must always be present. Besides, some input files (pseudopotentials, flags in the INCAR file, etc.) in the hands-on are old and shall be updated. See below.

Please update in the hands-on

• The energy cutoff is specified with ENCUT, not ENMAX or EMAX.
• The energy cutoff should be set in all INCAR files, and it should be consistent along all calculations for a given project. Please Use 500 for the hands-on.
• The comments in the INCAR file should be introduced with #, not !.
• POSCAR files should not include any comments.
• Use ISMEAR=0 (conductors&isolators). You may use ISMEAR=1 only for conductors, but it is not recommended. Avoid ISMEAR=2.
• The density functional should always be included in the INCAR file. Start with PBE (GGA = PE).
• The POSCAR file (VASP 5 and higher) lists the elements on line #6, which are omitted in the hands-on.
• For ionic relaxations, use force criteria, where EDDIF must be 1E-3 times lower than EDDIFG. (For energy criteria, 1E-1 would suffice).
• For frequency calculations, use between 1E-7 to 1E-8 eV per atom (eg, EDDIF 1E-5 would be OK for a large cell with 300 atoms).

Checklist

Before dealing with your first project, you must:

• Read Sholl&Steckel Density Functional Theory: A Practical Introduction.
• Complete the VASP hands-on.
• Know how to define the key flags in the INCAR file: density functional, energy cutoff, smearing, ionic algorithm, convergence criteria.
• Know what are the additional flags you need to include in the INCAR, depending on your system.
• Know where to get your pseudopotentials and which ones to select for each element.
• Know which kpoint density to use and if such number is already converged for your system.
• Learn to how to automate the generation of the POSCAR files. Many projects require automation.

For a more detailed understanding please refer to VASP documentation.

Additional tips are available here[1] (by Federico).