🔄 Format Conversion

GPUMDkit contains utilities for converting common atomistic simulation formats, with extra handling for metadata such as group labels, weights, and frame extraction.

What it does

This module converts structure and trajectory files between common formats used in computational materials science. It supports VASP, LAMMPS, CP2K, ABACUS, CIF, ASE trajectories, and extxyz. It also provides tools for adding group labels, weights, extracting frames, and replicating structures.

Before you start

Script location: Scripts/format_conversion/

Make sure GPUMDkit is installed. See Quick Start for installation instructions.

Supported formats

The format conversion module covers:

VASP: POSCAR, CONTCAR, OUTCAR, XDATCAR
LAMMPS: data files and dump trajectories
CP2K: output logs, position, force, and cell files
ABACUS: SCF/MD logs
CIF: crystallographic structure files
ASE trajectory: .traj
extxyz: a common structure format for GPUMD and NEP

Interactive Mode

Open GPUMDkit:

gpumdkit.sh

Choose:

1) Format Conversion

The format conversion menu is:

+-------------------------------------------------------------+
|                   FORMAT CONVERSION TOOLS                   |
+-------------------------------------------------------------+
| 101) VASP to extxyz            106) Add group labels        |
| 102) MTP to extxyz             107) Add weight to extxyz    |
| 103) CP2K to extxyz            108) Extract frame extxyz    |
| 104) ABACUS to extxyz          109) Clean XYZ info          |
| 105) extxyz to POSCAR          110) Replicate structure     |
+-------------------------------------------------------------+
| out2exyz) OUTCAR to extxyz     xdat2exyz) XDATCAR to extxyz |
| pos2exyz) POSCAR to extxyz     pos2lmp)   POSCAR to LAMMPS  |
| cif2pos)  CIF to POSCAR        lmp2exyz)  LAMMPS to extxyz  |
| cif2exyz) CIF to extxyz        traj2exyz) ASE traj to extxyz|
+-------------------------------------------------------------+
| 000) Return to main menu                                    |
+-------------------------------------------------------------+
Input the function number or converter keyword:

What Each Entry Does

Entry	Called script	Function	When to Use
`101`	`out2xyz.sh`	VASP OUTCAR to extxyz, shell version	convert VASP calculation directories
`102`	`mtp2xyz.py`	MTP cfg to extxyz	convert MTP training data
`103`	`cp2k_log2xyz.py` / `cp2k2xyz.py`	CP2K to extxyz	choose CP2K log/inp route or pos/frc/cell route
`104`	`abacus2xyz_scf.sh` / `abacus2xyz_md.sh`	ABACUS to extxyz	convert ABACUS SCF or MD output
`105`	`exyz2pos.py`	extxyz to POSCAR	write each extxyz frame as a POSCAR-style file
`106`	`add_groups.py`	add group labels	add atom group labels for GPUMD-related workflows
`107`	`add_weight.py`	add weights	assign training weights in extxyz
`108`	`get_frame.py`	extract frame	export one frame from an extxyz trajectory
`109`	`clean_xyz.py`	clean XYZ info	remove extra extxyz properties
`110`	`replicate.py`	replicate structure	build supercells by factors or target atom count
`out2exyz`	`out2exyz.py`	OUTCAR to extxyz, Python version	alternative VASP OUTCAR converter
`pos2exyz`	`pos2exyz.py`	POSCAR to extxyz	convert a single structure
`cif2pos`	`cif2pos.py`	CIF to POSCAR	prepare VASP input from CIF
`cif2exyz`	`cif2exyz.py`	CIF to extxyz	prepare GPUMDkit input from CIF
`xdat2exyz`	`xdatcar2exyz.py`	XDATCAR to extxyz	convert VASP MD trajectory
`pos2lmp`	`pos2lmp.py`	POSCAR to LAMMPS data	prepare LAMMPS input
`lmp2exyz`	`lmp2exyz.py`	LAMMPS dump to extxyz	convert LAMMPS trajectory
`traj2exyz`	`traj2exyz.py`	ASE traj to extxyz	convert ASE trajectory

Quick Command Reference

Source	Target	Command
OUTCAR directory	extxyz	`gpumdkit.sh -out2xyz <dir>`
OUTCAR directory	extxyz	`gpumdkit.sh -out2exyz <dir>`
POSCAR	extxyz	`gpumdkit.sh -pos2exyz <POSCAR> <output.xyz>`
extxyz	POSCAR files	`gpumdkit.sh -exyz2pos <input.xyz>`
XDATCAR	extxyz	`gpumdkit.sh -xdat2exyz XDATCAR dump.xyz`
POSCAR	LAMMPS data	`gpumdkit.sh -pos2lmp POSCAR lammps.data`
LAMMPS dump	extxyz	`gpumdkit.sh -lmp2exyz dump.lammpstrj Li Y Cl`
CIF	POSCAR	`gpumdkit.sh -cif2pos input.cif POSCAR.vasp`
CIF	extxyz	`gpumdkit.sh -cif2exyz input.cif model.xyz`
ASE traj	extxyz	`gpumdkit.sh -traj2exyz input.traj output.xyz`
extxyz	clean extxyz	`gpumdkit.sh -clean_xyz input.xyz clean.xyz`

Common Examples

Convert VASP calculations to extxyz

What it does: Searches a directory for VASP OUTCAR files and converts them into a single extxyz file for NEP training or analysis.

CLI mode:

gpumdkit.sh -out2xyz ./vasp_results/

The shell version searches the target directory and converts VASP results into an extxyz file. If you prefer the Python implementation:

gpumdkit.sh -out2exyz ./vasp_results/

Interactive mode: Choose 101 from the format conversion menu. You will see:

>-------------------------------------------------<
| Calling the script in Scripts/format_conversion |
| Script: out2xyz.sh                              |
| Developer: Yanzhou WANG (yanzhowang@gmail.com)  |
>-------------------------------------------------<
Input the directory containing OUTCARs
Example: ./
------------>>

Output: An extxyz file containing the converted structures, suitable for NEP training or further analysis.

Add group labels

What it does: Adds atom group labels to a structure file. Group labels are required by some GPUMD-related workflows, such as species-specific MSD or diffusion calculations.

CLI mode:

gpumdkit.sh -addgroup POSCAR Li Y Cl

This command reads the input structure and writes an extxyz file with group information.

Interactive mode: Choose 106 from the format conversion menu. You will see:

>-------------------------------------------------<
| Calling the script in Scripts/format_conversion |
| Script: add_groups.py                           |
| Developer: Zihan YAN (yanzihan@westlake.edu.cn) |
>-------------------------------------------------<
Input <POSCAR> <element1> <element2> ...
Example: POSCAR Li Y Cl
------------>>

Output: An extxyz file with group labels added.

Script Details

POSCAR to extxyz

gpumdkit.sh -pos2exyz POSCAR model.xyz

Use this when you have a single VASP structure and want an extxyz output.

Interactive keyword: pos2exyz

Input <POSCAR> <output.xyz>
Example: POSCAR model.xyz
------------>>

extxyz to POSCAR

gpumdkit.sh -exyz2pos structures.xyz

This converts all frames in an extxyz file into POSCAR_*.vasp files. Frame indices are 0-based in most GPUMDkit scripts, but output filenames are meant for direct inspection and batch calculations.

Interactive entry: 105

Input the name of extxyz
Example: ./train.xyz
------------>>

LAMMPS dump to extxyz

gpumdkit.sh -lmp2exyz dump.lammpstrj Li Y Cl

The element symbols must match the LAMMPS atom type IDs. For example, if type 1 is Li, type 2 is Y, and type 3 is Cl, the order should be Li Y Cl.

Interactive keyword: lmp2exyz

Input <dump_file> <element1> <element2> ...
Example: dump.lammpstrj Li O
------------>>

CIF conversion

gpumdkit.sh -cif2pos input.cif POSCAR.vasp
gpumdkit.sh -cif2exyz input.cif model.xyz

Use -cif2pos if you want a VASP-style structure, and -cif2exyz if the next step is GPUMDkit analysis.

Add weights

gpumdkit.sh -addweight train.xyz train_weighted.xyz 5

This is useful when you want some structures to have a different training weight in a NEP dataset.

Replicate structures

gpumdkit.sh -replicate POSCAR supercell.vasp 2 2 2
gpumdkit.sh -replicate POSCAR supercell.vasp 256

The first form uses explicit replication factors. The second form tries to build a supercell close to a target atom count.

Extract one frame

gpumdkit.sh -get_frame dump.xyz 1000

This extracts frame index 1000 from an extxyz trajectory.

Split multi-frame extxyz

split_single_xyz.py splits an extxyz file into individual frames, each written to a separate file.

python Scripts/format_conversion/split_single_xyz.py dump.xyz

This creates model_0.xyz, model_1.xyz, ... for each frame in the trajectory.

MTP conversion

Convert MTP .cfg format to extxyz:

gpumdkit.sh    # Select: 1) Format Conversion → 102

Interactive prompt:

Input <filename.cfg> <Symbol1 Symbol2 Symbol3 ...>
Example: train.cfg Pd Ag
------------>>

ABACUS conversion

Convert ABACUS output to extxyz:

gpumdkit.sh    # Select: 1) Format Conversion → 104

The menu offers two options:

SCF output (running_scf.log)
MD output (running_md.log)

Common Mistakes

Problem	What to Check
LAMMPS elements are wrong	Check the element order passed after the dump file
A trajectory has strange metadata	Try `-clean_xyz input.xyz clean.xyz`
A converted structure looks shifted	Inspect PBC/cell information in the source file
Frame extraction gives the wrong structure	Remember that frame indices are 0-based

Notes

If a Python package required by a specific converter is missing, Python will report it when that converter is used.