Poshcar - VASP POSCAR text editor package

Author: Andy Paul Chen (MSE, Nanyang Technological University)

Introduction

POSHCAR started as a cabin fever project during the first COVID lockdowns in the United States. It is a simple and lightweight text-based engine for generating and editing files in VASP format, which is one of the simplest and most compact descriptions of a crystal structures currently in use. The development follows an organic and modular development model where new functions are written whenever a project-specific need arises, so expect many changes as I hop from project to project.

How to use demo file

Demo notebooks are organised into 3 parts:
Core modules: Basic operations
Cell-building modules: Functions that lets you generate unit cells, e.g. supercells, organic molecules, slabs
Analytics: Functions involving statistical analysis of a unit cell, e.g. bonding behaviour

The output of the demo operations can be seen in the tests/_demo/ folder.

Modules

Interdependencies of modules are illustrated in the diagram below. The dependency relationship is marked with arrows (dependent -> core). Please use this graph for your reference if you would like to add to Poshcar!

Dependencies

ase, pyvis, rdkit, scipy, pymatgen, chgnet, pandas, networkx

How to install

PyPI release: pip install poshcar
Current github instance: pip install git+https://github.com/andypaulchen/poshcar.git
Developer install (FAFO) version: Download the package, cd to the folder where setup.py is, and then run the edit mode pip install (pip install -e .).

Changelog

You can visit the changelog in docs/changelog.txt for a short summary of changes I made over the years. I'm a bit lazy in the documentation, though.
Current version: 2.1.1
Last update: 19 January 2026