IMAGES
IMAGES = [integer]
Default: IMAGES = 0
Description: IMAGES defines the number of instances of VASP initiated. These instances carry out VASP calculations in separate directories (e.g., 01, 02, 03, etc.). This flag is instrumental in supporting various calculations including elastic band calculations, parallel tempering, and thermodynamic integration, where simultaneous execution of multiple VASP instances is necessary.
VASP supports different modes for performing simultaneous calculations using distinct INCAR, KPOINTS, POTCAR, or POSCAR files. These modes include the elastic band method for energy barrier calculations, thermodynamic coupling-constant integrations, and parallel tempering. Typically, the primary INCAR file should be located in the root directory. Other files such as KPOINTS, POTCAR, and POSCAR can be placed in subdirectories (e.g., 00, 01, 02...) or in the root directory. Files in subdirectories take precedence over those in the root directory.
File handling
When VASP is started, it reads the file INCAR in the root directory. The following tags are also read from the root INCAR file: NCORE_IN_IMAGES1, IMAGES, KIMAGES, FOURORBIT, KPAR, NCORE, NCORES_PER_BAND, NPAR, NCSHMEM. Subsequently, VASP splits the MPI communicator into subgroups and continues reading from the INCAR file in the subdirectories 01, 02, 03, ... If the INCAR files are not present in the subdirectories, VASP continues reading from the root INCAR file. The same logic is used from the files KPOINTS and POTCAR: if they exist in the subdirectories, they will be read from the subdirectories; if they are missing, the files are read from the root directory. The POSCAR file and all other input files are always read from the subdirectories 01, 02, etc.. All output files (including OUTCAR and OSZICAR) are always written to the subdirectories. For the nudged elastic band method, it is recommended that all input files, except the POSCAR, WAVECAR and CHGCAR file, reside in the root directory.
Parallel Tempering (LTEMPER tag):
Use cases
- Nudged elastic bands
- If IMAGES is set without any other tag, an elastic-band calculation is performed. This defaults to the recommended nudged-elastic-band method but other options are available by modifying the SPRING tag. Please consider the nudged-elastic-bands how to and the SPRING tag for more information.
- Thermodynamic coupling-constant integrations
- When VCAIMAGES is set in the INCAR file, VASP computes a thermodynamic coupling-constant integration. This in turn sets IMAGES=2 running two VASP calculations in the subdirectories 01 and 02. Since this is a special case where the two calculations may have different computational cost, NCORE_IN_IMAGE1 can be set to force an unequal split of the processes across the two images. The tag VCAIMAGES describes in more details how to setup these calculations.
- Parallel tempering
- If the tag LTEMPER=.TRUE. is set in the INCAR file, VASP performs parallel tempering calculations. In this case, it is necessary to provide different POSCAR files in each subdirectory and modify the TEBEG either by separate INCAR files or nested IMAGE_X/TEBEG definitions in the root INCAR file. For further details, refer to the description of the LTEMPER tag.
Related tags and articles
SPRING, IBRION, NFREE, SMASS, VCAIMAGES, LTEMPER