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{{TAGDEF|IMAGES|[integer]|0}}
{{TAGDEF|IMAGES|[integer]|0}}


Description: {{TAG|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.
Description: Defines the number of VASP calculations in separate directories, (e.g., 01, 02, 03, etc.) for [[Nudged elastic bands|nudged elastic band]] calculations, [[LTEMPER|parallel tempering]], and [[VCAIMAGES|thermodynamic integration]].
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VASP supports different modes for performing simultaneous calculations using distinct INCAR, KPOINTS, POTCAR, or POSCAR files.
{{TAG|IMAGES}} sets the number of independent VASP calculations in separate directories. The primary {{FILE|INCAR}} file should be located in the root directory.
These modes include the elastic band method for energy barrier calculations, thermodynamic coupling-constant integrations, and parallel tempering.
Other files such as {{FILE|KPOINTS}}, {{FILE|POTCAR}}, and {{FILE|POSCAR}} can be placed in subdirectories, e.g., 01, 02, 03, etc., or in the root directory. Files in subdirectories take precedence over those in the root directory.
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.


See [[#Use cases|use cases]] described below.
== File handling ==
== File handling ==
When VASP is started, it reads the file {{TAG|INCAR}} in the root directory.
When VASP starts, it reads the file {{FILE|INCAR}} in the root directory.
The following tags are also read from the root {{TAG|INCAR}} file:
Subsequently, VASP splits the MPI communicator into subgroups for each image.
{{TAG|NCORE_IN_IMAGES1}}, {{TAG|IMAGES}}, {{TAG|KIMAGES}}, {{TAG|FOURORBIT}}, {{TAG|KPAR}}, {{TAG|NCORE}},
If an {{FILE|INCAR}} file is present in the subdirectories 01, 02, 03, ..., VASP will process those afterward.
{{TAG|NCORES_PER_BAND}}, {{TAG|NPAR}}, {{TAG|NCSHMEM}}. Subsequently, VASP  
Otherwise, VASP continues reading from the root {{FILE|INCAR}} file.
splits the MPI communicator into subgroups and continues reading from the {{TAG|INCAR}}
You can also provide image-specific data in the root {{FILE|INCAR}} file if the files are very similar
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 {{TAG|KPOINTS}} and {{TAG|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 {{TAG|POSCAR}} file and all other input files
are always read from the subdirectories 01, 02, etc..
All output files (including {{TAG|OUTCAR}} and {{TAG|OSZICAR}}) are always written to the subdirectories.
For the nudged elastic band method, it is recommended that all input files, except the {{TAG|POSCAR}}, {{TAG|WAVECAR}} and {{TAG|CHGCAR}} file, reside in the root directory. 


Parallel Tempering (LTEMPER tag):
  # general INCAR tags
  IMAGES = 4
  TEBEG = 600
 
  # INCAR tags only on IMAGE 1
  IMAGE_1 {
    TEBEG = 400
  }
 
  # INCAR tags only on IMAGE 2
  IMAGE_2 {
    TEBEG = 500
  }


Here, images 3 and 4 would use {{TAG|TEBEG}}=600 because the value is not specified for the image.
The files {{TAG|KPOINTS}} and {{TAG|POTCAR}} will be read from the subdirectory if available and from the root directory otherwise.
The {{TAG|POSCAR}} file and all other input files are always read from the subdirectories.
All [[:Category:Output files|output files]] (including {{TAG|OUTCAR}} and {{TAG|OSZICAR}}) are always written to the subdirectories.


To summarize, to run a calculation with {{TAG|IMAGES}}, you provide:
* an {{FILE|INCAR}} file in the root directory
* optionally an overwriting {{FILE|INCAR}} file in the subdirectories
* {{FILE|POSCAR}} files in the subdirectories
* {{FILE|KPOINTS}} and {{FILE|POTCAR}} either in the root or in the subdirectories


== Use cases ==
== Use cases ==


; Nudged elastic bands
; Nudged elastic bands
: If {{TAG|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 {{TAG|SPRING}} tag. Please consider the [[Nudged elastic bands|nudged-elastic-bands how to]] and the {{TAG|SPRING}} tag for more information.
: If {{TAG|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 {{TAG|SPRING}} tag. Please consider the [[Nudged elastic bands|nudged-elastic-bands how-to]] and the {{TAG|SPRING}} tag for more information.


; Thermodynamic coupling-constant integrations
; Thermodynamic coupling-constant integrations
: When {{TAG|VCAIMAGES}} is set in the {{FILE|INCAR}} file, VASP computes a thermodynamic coupling-constant integration. This in turn sets {{TAG|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, {{TAG|NCORE_IN_IMAGE1}} can be set to force an unequal split of the processes across the two images. The tag {{TAG|VCAIMAGES}} describes in more details how to setup these calculations.
: When {{TAG|VCAIMAGES}} is set in the {{FILE|INCAR}} file, VASP computes a thermodynamic coupling-constant integration. This, in turn, sets {{TAG|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 costs, {{TAG|NCORE_IN_IMAGE1}} can be set to force an unequal split of the processes across the two images. The tag {{TAG|VCAIMAGES}} describes in more detail how to set up these calculations.
 
; Parallel tempering
: If the tag {{TAG|LTEMPER}}=.TRUE. is set in the {{FILE|INCAR}} file, VASP performs parallel tempering calculations. In this case, it is necessary to provide different {{FILE|POSCAR}} files in each subdirectory and modify the {{TAG|TEBEG}} either by separate {{FILE|INCAR}} files or nested IMAGE_''X''/{{TAG|TEBEG}} definitions in the root {{FILE|INCAR}} file. For further details, refer to the description of the {{TAG|LTEMPER}} tag.


; Parallel tempering/replica-exchange method and performing independent calculations
: If the tag {{TAG|LTEMPER}}=.TRUE. is set in the {{FILE|INCAR}} file, VASP will perform parallel tempering calculations. In this case, it is necessary to provide different {{FILE|POSCAR}} files in each subdirectory and modify the {{TAG|TEBEG}} either by separate {{FILE|INCAR}} files or nested IMAGE_''X''/{{TAG|TEBEG}} definitions in the root {{FILE|INCAR}} file. For further details, refer to the description of the {{TAG|LTEMPER}} tag. The combination {{TAG|LTEMPER}}=.TRUE. and {{TAG|NTEMPER}}=0, also allows to run entirely independent calculations in the individual subdirectories. This might be helpful to make better use of nodes with many cores.


== Related tags and articles ==
== Related tags and articles ==
{{TAG|SPRING}},
{{TAG|IBRION}},
{{TAG|NFREE}},
{{TAG|SMASS}},
{{TAG|VCAIMAGES}},
{{TAG|VCAIMAGES}},
{{TAG|LTEMPER}}
{{TAG|LTEMPER}},
[[Nudged elastic bands|nudged-elastic-bands how-to]],
{{TAG|SPRING}}


{{sc|IMAGES|Examples|Examples that use this tag}}
{{sc|IMAGES|Examples|Examples that use this tag}}
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[[Category:INCAR tag]][[Category:Transition States]][[Category:Elastic band method]][[Category:Parallelization]]
[[Category:INCAR tag]][[Category:Transition states]][[Category:Parallelization]]

Latest revision as of 16:41, 12 March 2024

IMAGES = [integer]
Default: IMAGES = 0 

Description: Defines the number of VASP calculations in separate directories, (e.g., 01, 02, 03, etc.) for nudged elastic band calculations, parallel tempering, and thermodynamic integration.


IMAGES sets the number of independent VASP calculations in separate directories. 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., 01, 02, 03, etc., or in the root directory. Files in subdirectories take precedence over those in the root directory.

See use cases described below.

File handling

When VASP starts, it reads the file INCAR in the root directory. Subsequently, VASP splits the MPI communicator into subgroups for each image. If an INCAR file is present in the subdirectories 01, 02, 03, ..., VASP will process those afterward. Otherwise, VASP continues reading from the root INCAR file. You can also provide image-specific data in the root INCAR file if the files are very similar

 # general INCAR tags
 IMAGES = 4
 TEBEG = 600
 
 # INCAR tags only on IMAGE 1
 IMAGE_1 {
   TEBEG = 400
 }
 
 # INCAR tags only on IMAGE 2
 IMAGE_2 {
   TEBEG = 500
 }

Here, images 3 and 4 would use TEBEG=600 because the value is not specified for the image. The files KPOINTS and POTCAR will be read from the subdirectory if available and from the root directory otherwise. The POSCAR file and all other input files are always read from the subdirectories. All output files (including OUTCAR and OSZICAR) are always written to the subdirectories.

To summarize, to run a calculation with IMAGES, you provide:

  • an INCAR file in the root directory
  • optionally an overwriting INCAR file in the subdirectories
  • POSCAR files in the subdirectories
  • KPOINTS and POTCAR either in the root or in the subdirectories

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 costs, NCORE_IN_IMAGE1 can be set to force an unequal split of the processes across the two images. The tag VCAIMAGES describes in more detail how to set up these calculations.
Parallel tempering/replica-exchange method and performing independent calculations
If the tag LTEMPER=.TRUE. is set in the INCAR file, VASP will perform 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. The combination LTEMPER=.TRUE. and NTEMPER=0, also allows to run entirely independent calculations in the individual subdirectories. This might be helpful to make better use of nodes with many cores.

Related tags and articles

VCAIMAGES, LTEMPER, nudged-elastic-bands how-to, SPRING

Examples that use this tag