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


Description: {{TAG|IMAGES}} defines how many instances of VASP are started. These instances execute VASP calculations in separate directories 01, 02, 03, etc. This flag is used to support elastic band calculations, parallel tempering, thermodynamic integration as well as other scenaria where a simultaneous calculation of several VASP instances is required.
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.
 
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VASP supports various modes where simultaneous calculations for different INCAR, KPOINTS, POTCAR, or POSCAR file are performed.
The elastic band method to calculate energy barriers, as well as parallel tempering are explained in this section.
Generally a primary  {{TAG|INCAR}} file must be located in the root directory. Most of the other files, including {{TAG|KPOINTS}}, {{TAG|POTCAR}}, {{TAG|POSCAR}} can either reside in the subdirectories (named 00, 01, 02...) or in the root directory.
The files in the subdirectories take precedence over those in the root directory (for details
see the paragraph "File handling" below). The tag
{{TAG|IMAGES}} = number of images
forces VASP to execute multiple instances, performing calculations in the subdirectors 01, 02, .., number of images.
The number of nodes must be dividable by the number of images (the tags {{TAG|NCORE}}, {{TAG|KPAR}} or {{TAG|NPAR}} can still be use and might even be different, if INCAR files are supplied in the subdirectories).
VASP divides the nodes in groups, and each group then works on one ''image'' 01, 02, ... IMAGES.
For nudged elastic band calculations, it is usually sufficient to provide all input files in the root directory,
except for the POSCAR files which need to be provided in the subdirectories.
The first group of nodes will then read the {{TAG|POSCAR}} file from  the directory 01, the second group from 02 etc.
In the elastic band method, the endpoints are kept fixed, and the position
of the end points must be supplied in the files 00/POSCAR and XX/POSCAR, where  XX is
XX = number of images+1.
(the directories 00 and XX are only required for elastic band calculations).
If the tag {{TAG| LTEMPER}}=.TRUE. is set in the {{TAG| INCAR}} file, VASP performs parallel tempering calculations. In this case, it is necessary to supply different {{TAG| INCAR}} and {{TAG| POSCAR}} files in each subdirectory. For each subdirectory a different simulation temperature should be supplied using the tags  {{TAG| TEBEG}} in the INCAR files of the subdirectories. For further details, we refer to the description of the tag {{TAG| LTEMPER}}.
All output files ({{TAG|OUTCAR}}, {{TAG|WAVECAR}}, {{TAG|CHGCAR}} etc.) are all written to the subdirectories.
Since no nodes are executing for the positions supplied in the
directories 00 and XX, no output files will be created in these sub directories.
Image 01 writes to the usual stdout file, located in the directory from which VASP is started,
the other images write to the files 02/stdout, 03/stdout etc.
In addition to the {{TAG|IMAGES}} tag, a spring constant can be
supplied in the {{TAG|SPRING}} tag. The default is
{{TAG|SPRING}}= -5
The '''nudged elastic band method'''<ref name="jons95"/><ref name="jons98"/> is applied
when {{TAG|SPRING}} is set to a negative value, e.g.
{{TAG|SPRING}}= -5. This is also the recommended setting.
Compared to the previous case, additional tangential springs
are introduced to keep the images equidistant
during the relaxation (remember the constraint is only
conserved to first order otherwise). Do not use too large values,
because this can slow down convergence. The default value
usually works reliably.
One problem of the nudged elastic band method is
that the constraint (i.e movements only
in the hyper-plane perpendicular to the current tangent) is
non linear. Therefore, the CG algorithm usually fails
to converge, and  we recommended to use
the RMM-DIIS algorithm ({{TAG|IBRION}}=1) or the quick-min algorithm ({{TAG|IBRION}}=3).
Additionally,
the non-linear constraint (equidistant images) tends to be  violated
significantly during the first few steps (it is only enforced to first order).
If this problem is
encountered, a very low dimensionality parameter ({{TAG|IBRION}}=1, {{TAG|NFREE}}=2)
should be applied in the first few steps, or a steepest
descent minimization without line optimization ({{TAG|IBRION}}=3, {{TAG|SMASS}}=2).
should be used, to  pre-converge the images.


If all degrees of freedom are allowed to relax (isolated
VASP supports different modes for performing simultaneous calculations using distinct INCAR, KPOINTS, POTCAR, or POSCAR files.
molecules, no surface, etc.), make sure that
These modes include the elastic band method for energy barrier calculations, thermodynamic coupling-constant integrations, and parallel tempering.
the sum of all positions  is the same for each cell. In other words,
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.


<math> \sum_{i=1,N_{ions}} \vec R_i^{\alpha} </math>
== File handling ==
 
When VASP is started, it reads the file {{TAG|INCAR}} in the root directory.
must be equal for all images. Otherwise ''fake'' forces
are introduced, and the images drift against
each other (this will not introduce problems
during the VASP calculations, but it is awkward to visualize
the final results).
Often an initial linearly interpolated  starting guess is
appropriate, this can e.g. be done with a small script called
interpolatePOS
The script also removes as an option the center-of-mass motion.
 
Finally, we strongly recommend to keep the number of images
to an absolute minimum. The fewer images are used, the faster
to convergence to the groundstate is. Often, it is
advisable to start with a single image between the two endpoints,
and to increase the number of images, once this first run has converged.
 
<!-- This should become a specialized form of the short description in the parallelization
File handling: When VASP is started, it reads the file {{TAG|INCAR}} in the root directory.  
The following tags are also read from the root {{TAG|INCAR}} file:
The following tags are also read from the root {{TAG|INCAR}} file:
{{TAG|NCORE_IN_IMAGES1}}, {{TAG|IMAGES}}, {{TAG|KIMAGES}}, {{TAG|FOURORBIT}}, {{TAG|KPAR}}, {{TAG|NCORE}},  
{{TAG|NCORE_IN_IMAGES1}}, {{TAG|IMAGES}}, {{TAG|KIMAGES}}, {{TAG|FOURORBIT}}, {{TAG|KPAR}}, {{TAG|NCORE}},  
Line 89: Line 20:
if they exist in the subdirectories, they will be read from the subdirectories; if they
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 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 read from the subdirectories 01, 02, etc..  
are always written to the subdirectories.  
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.   
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):


IMAGES Parameter:


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 Modes for Simultaneous Calculations:


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 and parallel tempering, both of which are detailed in this section.
== Use cases ==
File Handling:


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. For further details, refer to the "File Handling" section below.
; Nudged elastic bands
Parallel Tempering (LTEMPER tag):
: 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
: 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.
 
; 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.


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 INCAR and POSCAR files in each subdirectory, along with distinct simulation temperatures using the TEBEG tag in the INCAR files of the subdirectories. For further details, refer to the description of the LTEMPER tag.


== Related tags and articles ==
== Related tags and articles ==
{{TAG|SPRING}},
{{TAG|SPRING}},
{{TAG|NPAR}},
{{TAG|IBRION}},
{{TAG|IBRION}},
{{TAG|NFREE}},
{{TAG|NFREE}},
{{TAG|SMASS}},
{{TAG|SMASS}},
{{TAG|VCAIMAGES}}
{{TAG|VCAIMAGES}},
{{TAG|LTEMPER}}


{{sc|IMAGES|Examples|Examples that use this tag}}
{{sc|IMAGES|Examples|Examples that use this tag}}


== References ==
<references>
<ref name="jons95">[http://dx.doi.org/10.1016/0039-6028(94)00731-4 G. Mills, H. Jonsson and G. K. Schenter, Surface Science, 324, 305 (1995).]</ref>
<ref name="jons98">H. Jonsson, G. Mills and K. W. Jacobsen,
''Nudged Elastic Band Method for Finding Minimum Energy Paths of Transitions'',
in ''Classical and Quantum Dynamics in Condensed Phase Simulations'',
ed. B. J. Berne, G. Ciccotti and D. F. Coker (World Scientific, 1998).</ref>
</references>
----
----


[[Category:INCAR tag]][[Category:Transition States]][[Category:Elastic band method]][[Category:Parallelization]]
[[Category:INCAR tag]][[Category:Transition States]][[Category:Elastic band method]][[Category:Parallelization]]

Revision as of 10:31, 19 October 2023

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

Examples that use this tag

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