CELL File

What are CELL files and how to open them

Are you having problems opening a CELL file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your CELL files.

What is a CELL file?

A .CELL file is a CASTEP Cell Structure Info file.

A CASTEP Cell Structure Info file holds all the details needed to define a material (or molecular) structure for computation in the CASTEP package. It is used as input when setting up simulations of crystal lattices: it specifies the lattice type and vectors, the atoms' positions within the lattice, the pseudopotentials for each atomic species, and other structural settings needed before CASTEP performs calculations. CASTEP requires one of these files plus a separate parameter file to define a full calculation.

This file is a plain-text, keyword- and block-driven format. Blocks begin with %BLOCK <name> and must end with %ENDBLOCK <name>. At minimum it must include a lattice block (either Cartesian vectors or lengths + angles) and an atomic‐positions block (either fractional or absolute coordinates). Other optional blocks allow specification of k-point grids, external pressure, symmetry operations, atomic species masses and pseudopotentials, and constraints on atoms or cell shape. Keywords and blocks may appear in any order.

Internal identifiers aid recognition: for example, the format includes block names like %BLOCK POSITIONS_FRAC, %BLOCK SPECIES_POT, %BLOCK LATTICE_CART or %BLOCK LATTICE_ABC, and keywords such as KPOINT_MP_GRID, SYMMETRY_GENERATE, or _MP_GRID, together with end markers like %ENDBLOCK POSITIONS_FRAC. These signatures appear at fixed offsets in the file or as contained strings, enabling tools to detect this format reliably.

How to open CELL files

Important: Different programs may use files with the CELL file extension for different purposes, so unless you are sure which format your CELL file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested four different CELL openers which you will find listed below.

Last updated: August 31, 2026

Various apps that use files with this extension

These apps are known to open certain types of CELL files. Remember, different programs may use CELL files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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