Notice: We are excited to announce that version 1.1.1 of kpLib is now available. In this release, we have made the Python interface more flexible by allowing structures to be passed in as plain Python lists or Numpy arrays. This gives users the option to choose their preferred structure parser. Bugs were also fixed that could cause the Python interface to hang without output. Users can upgrade from the source code on gitlab or from the PyPI index. For details of the change and documentaion of the updated interface, please refer to the README of our gitlab repository.
KpLib is a lightweight, open-sourced C++ library for searching and generating optimal generalized k-point grids for efficient integration in reciprocal space during electronic structure calcualtions. It implements novel algorithms that allow fast generation of highly efficient generalized k-point grids on-the-fly, without querying a database. We choose C++ as the programming language to assist integration with existing electronic structure codes.
To use the library, users can compile the source code and link the binaries as a common C++ library. A cmake script is provided to automate the compilation, and a simple application is shipped together with the source code to demonstrate the usage of the API. A python wrapper is also provided for python users with the help of Dr. Shyam Dwaraknath from LBNL. It is released as a package on PyPI under the name kpLib, and can be quickly installed using pip. Users can either import it as a module or use the terminal command kpGen it provides. If both the C++ API and the python wrapper don't fit your needs, you can customize your own wrapper functions easily, given that the source code uses primarily elementary data structures and has only 1122 lines,
KpLib is open-sourced at: https://gitlab.com/muellergroup/kplib. Detailed documentation of the API and its usage can be found at the homepage of the repository.
For explanations of our algorithms underlying the dynamic generation approach implemented in kpLib, users are encouraged to read our recent paper.
To receive updates and announcements regarding kpLib, the K-Point Grid Generator (see below), and the K-Point Server (see below), please subscribe to the kpoints-announce mailing list.
Please contact us at firstname.lastname@example.org if you encounter any difficulties.
A stand-alone version of the K-point Grid Server has been created and tested. It can be used as a local application, and provides the same functionality as the current version of the server. Updates of K-point Server is synchronized with K-point Grid Generator (i.e. all updates on K-point Server will be mirrored in K-point Grid Generator.)
A pre-built executable jar is available. To use the application, please download the tarball:
To configure the application, users need to set the variable "JAR_PATH", in the modified getKPoints script to the location where you have put the executable jar, and change the "CALL_SERVER_IF_LOCAL_MISSING" to "TRUE" if you want the script to call the server when the local program failed to be executed for some reasons. Then you can copy the script to ~/bin, and use it as any other Linux commands. We have included an instruction in the tarball for users reference.
A new database has been published on 2019.08.01. The new database is not compatible with previous version of the K-Point Grid Generator. The version number (date of release) is included in the database file names to remind users of the version of the database they are using, and a check is enforced in the code to ensure the code and database is compatible.
K-point Grid Generator is open-sourced at: https://gitlab.com/muellergroup/k-pointGridGenerator
Details about how pre-generated k-point grids are organized in the database and how K-point Grid Generator search and retrieve grids from the database are available in the Supplementary Information of our recent paper.
To make use of all of the features of server versions 2020.11.25 and later, it is necessary to use the getKPoints script version C2020.11.25 or later. Script earlier than C2020.11.25 could leave an emtpy KPOINTS when the latest server encounters an error in generating valid grids, such as incorrect MAGMOM in INCAR. Users are encouraged to upgrade to this new script. A warning will be printed to remind user that an outdated script is in use when the server detects it.
The k-point grid server provides efficient k-point grids for Brillouin zone integration. We estimate that on average the use of these grids accelerates well-converged calculations by a factor of about 2 compared to conventional methods for generating Monkhorst-Pack grids.
To use the server, please download the following files:
getKPoints is a Bash script that should work on most Unix and Linux systems. To generate k-point grids using getKPoints, it needs to have execution permission and be called from the directory where the calculation input files are located. We recommend you put it somewhere in your PATH. For example, if getKPoints is placed in the directory where the input files are located, then calling:
will automatically generate the k-point grids for the given input files. Currently, only VASP input file formats are supported. However, we are working to expand the support for other software.
The PRECALC file should be placed in the same directory as the rest of your input files. If the PRECALC file cannot be found, default values will be used. The available parameters for the PRECALC file are:
|TRUE / FALSE / AUTO
|Determines if the grid will contain the gamma point. AUTO selects the grid with the smallest number of irreducible k-points.
|The minimum allowed distance between lattice points on the real-space superlattice (rmin in our paper). This determines the density of the k-point grid.
|The minimum allowed number of total k-points in the Brillouin zone.
| The minimum allowed number of k-points
per reciprocal atom.
We do not advise setting a value for KPPRA for systems with less than three periodic dimensions. For example, if KPPRA were used to set the k-point density for a two-dimensional slab, doubling the thickness of the slab would cut the density of the k-point grid roughly in half. This is probably not the desired behavior. In this case, we recommend using MINDISTANCE instead.
|This parameter is used to auto-detect slabs, nanowires, and nanoparticles. If there is a gap (vacuum) that is at least GAPDISTANCE wide in the provided structure, the k-point density in the corresponding direction will be reduced accordingly.
|NONE / STRUCTURAL/ TIME_REVERSAL/ ALL
|An optional flag to control the symmetry operations that reduces the k-point grid. The default value, NONE, will try to maximize the number of symmetry operations used to reduce the k-point grid based on the provided input files. STRUCTURAL removes all structural symmetry operations when generating the grid, retaining only time-reversal symmetry. TIME_REVERSAL removes time-reversal symmetry, retaining only structural symmetry. ALL removes all symmetry operations from consideration, so symmetry is not used to reduce the k-point grid.
|This parameter controls the upper limit of the size of the grids that are searched before using a scale factor for triclinic structures. Generally speaking, a larger value will result in more extensive searches for k-point grids in some cases, which may return a better k-point grid but may also take more time. A larger value will also increase the maximum number of total k-points the server can return for triclinic structures. This flag only affects triclinic systems and is preferred over LOW_SYMMETRY_SEARCH_DEPTH.
|This parameter controls the upper limit of the size of the grids that are searched before using a scale factor for monoclinic structures. Generally speaking, a larger value will result in more extensive searches for k-point grids in some cases, which may return a better k-point grid but may also take more time. A larger value will also increase the maximum number of total k-points the server can return for monoclinic structures. This flag only affects monoclinic systems and is preferred over LOW_SYMMETRY_SEARCH_DEPTH.
|This parameter controls the upper limit of the size of the grids that are searched before using a scale factor for triclinic and monoclinic structures. Generally speaking, a larger value will result in more extensive searches for k-point grids in some cases, which may return a better k-point grid but may also take more time. This flag only affects triclinic and monoclinic systems. This flag is deprecated since version 2019.06.14 and will be removed in future releases. It is overriden by MONOCLINIC_SEARCH_DEPTH and TRICLINIC_SEARCH_DEPTH if they are present.
|VERBOSE / SIMPLE
|Sets the verbosity of the grid information written to the file.
|TRUE / FALSE
|If TRUE, generating basis vectors of a grid will be written in KPOINTS. Otherwise, explicit list of k-points will be used. Note this parameter is exclusively meant for VASP.6 and later versions. It could lead to incorrect results for VASP versions earlier than 6. Using the format of generating vectors can be espeically beneficial for calculations in which k-points weights may be adjusted, such as calculations of phonon. It also allow tetrahedron integration (ISMEAR=-5) in VASP without providing a connection table. When TRUE, generating vectors will also be printed to screen in addition to be saved to KPOINTS. When FALSE, list of k-points will be directly saved to KPOITNS without being printed out to standard output.
*If the PRECALC file does not include at least one of MINDISTANCE, MINTOTALKPOINTS, or KPPRA, then MINDISTANCE=28.1 will be used to determine grid density.
Below is an example of a PRECALC file:
The selection of MINDISTANCE (rmin in our paper) determines the density of the k-point grid generated. The number of k-points in the returned grid will scale roughly as MINDISTANCEd, where "d" is the number of periodic dimension (e.g. d=3 for bulk materials and d=2 for slab calculations). To get the best performance, we recommend you select a value of MINDISTANCE carefully. Listed in the table below are good starting values for MINDISTANCE for a given metal / non-metal and a desired calculation accuracy. Please note that the values below are provided for reference purposes only and the only way to know for sure whether the desired accuracy has been achieved or not is by testing it.
|MINDISTANCE for Metals
|MINDISTANCE for Non-Metals
|1 meV / atom
|3 meV / atom
|10 meV / atom
MINDISTANCE (rmin) can be
related to other parameters used to specify the minimum grid
density: k-points per
reciprocal atom (kAtom), k-points
per reciprocal cubic Angstrom (kVol), and the length of the longest
vector in the Minkowski-reduced representation of the k-point
lattice in reciprocal space (kDist). To do this, we match the
percentage of calculations that converge for a given level of
accuracy for different different parameters. The comparison is shown
below (click image to enlarge):
Additional details and benchmark information can be found in our paper.
If you would like to use k-point Grid Server, k-point Grid Generator or kpLib, please cite the following papers:
The version history for the server can be found here.
The version history for the client can be found here.
To receive updates and announcements regarding the k-point server, please subscribe to the kpoints-announce mailing list.
If you have any questions or comments, please contact us at email@example.com.