A python module for manipulating cartesian and internal coordinates.
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chemcoord: A python module for coordinates of molecules

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The project's website with documentation is: http://chemcoord.readthedocs.org/


  • Molecules are reliably transformed between cartesian space and non redundant internal coordinates (Zmatrices). Dummy atoms are inserted and removed automatically on the fly if necessary.
  • The created Zmatrix is not only a structure expressed in internal coordinates, it is a "chemical" Zmatrix. "Chemical" Zmatrix means, that e.g. distances are along bonds or dihedrals are defined as they are drawn in chemical textbooks (Newman projections).
  • Analytical gradients for the transformations between the different coordinate systems are implemented.
  • Performance intensive functions/methods are implemented with Fortran/C like speed using numba.
  • Geometries may be defined with symbolic expressions using sympy.
  • Built on top of pandas with very similar syntax. This allows for example distinct label or row based indexing.
  • It derived from my own work and I heavily use it during the day. So all functions are tested and tailored around the work flow in theoretical chemistry.
  • The classes are safe to inherit from and can easily be customized.
  • It as a python module ;)

Installation guide

A working python installation is required (2.7 and >=3.5 are possible).

It is highly recommended to use this module in combination with Ipython and jupyter. They come shipped by default with the anaconda3 installer


For the packaged versions, the following commands have to be executed in the terminal:

conda install -c mcocdawc chemcoord


pip install chemcoord

For the up to date development version (experimental):

git clone https://github.com/mcocdawc/chemcoord.git
cd chemcoord
pip install .


Neither installation nor running the module are tested on windows. To the best of my knowledge it should work there as well. Just use the same steps as for UNIX.


The changelog can be found here.

Citation and mathematical background

If chemcoord is used in a project that leads to a scientific publication, please acknowledge this fact by citing Oskar Weser (2017) using this ready-made BibTeX entry:

author = {Oskar Weser},
title = {An efficient and general library for the definition and use of internal coordinates in large molecular systems},
school = {Georg August Universität Göttingen},
year = {2017},
month = {November},

The master thesis including the derivation of implemented equations and the mathematical background can be found here.