i-PI is an open source project, and everyone is welcome to contribute with bug fixes, documentation, examples, new features, regression tests, etc. Any contribution from users or developers is very much welcome! These contributions may be full new methods/algorithms that you have developed or that you just would like to add to i-PI, or simple improvements (that would make your life easier) regarding the code itself, the documentation, or analysis scripts.

Useful resources

For more information on i-PI in general please consult the following places:

What we expect from a contribution

To start contributing, note the following general guidelines:

  • Your contribution should be based on the main branch of the repository

  • We expect you to fork the repository and make all the changes in your fork

  • When done, you can open a pull request (PR) to our repository, which will be reviewed.

For a PR to be issued, we will expect that:

  • You have produced code that is compliant with our formatting requirements (black and flake8, as explained in the README here:

  • You have written understandable docstrings for all functions and classes you have created

  • For all contributions (bug fixes, new functionalities, etc.), ensure that the continuous integration tests all pass.

  • In case of a new functionality:

    • You have added an example to the examples folder that showcases it. The inputs should be a simple but meaningful example of the functionality.

    • You have added a regression test to i-pi/ipi_tests/regression_tests folder (more on this below).

Creating a regression test

If you code up a new functionality, it is best that it goes directly to the regression test infrastructure, so that we can ensure that it does not break with future code restructuring or the addition of new features in the future. The information below can also be found in the README file in the i-pi/ipi_tests/regression_tests folder:

To add a new regression test please provide:

  • input.xml (and all the files required by it)

  • test_settings.dat This file specifies the driver_model and flags that will be used when running the driver to perform the regression test. For examples including the usage of option flags, please see:

    tests/NVE/NVE_1/harmonic_python/test_settings.dat tests/NVE/NVE_1/harmonic/test_settings.dat

    If your regtest uses a new driver mode, please add it to the fortran_driver_models list in the i-pi/ipi_tests/ file.

  • file_to_check.txt specifying the files serving as reference with their respective filenames. For an existing example, please see:


  • reference files that are listed in the files_to_check.txt file. Currently, the available formats are .xyz and numpy-accessible which should be specified with the keywords ‘xyz’ and ‘numpy’.

Important points to note:

  • In the case of multiple drivers needed for a simulation, the test_settings.dat file has to include a line for each driver by specifying as many lines as needed of driver_model xxxx in the order they should be assigned to the sockets. That is followed by lines decribing the corresponding flags of each driver.

  • The extension *.out appears in the .gitignore file. This means that the ‘ref_simulation.out’ file has to be added manually to your commit. You can do that by typing: “git add -f ref_simulation.out”

If you are developing something new and you are unsure about how to proceed, we encourage opening an issue with your question. Depending on the development, we can open a channel of discussion with the core developers (Slack) in order to see how to best handle your case!

Adding features involving a client code

If your new development in i-PI is directly related to a specific client code or if there is the need of coding a new native client in i-PI there can be some further adjustments to do. We very much welcome new interfaces and we will be happy to answer your questions.

If you want to enable the communication of a new client code with i-PI, it is not difficult: Please check an example of how it was done in fortran and python in the drivers folder in the repository.

Getting recognition for your contribution

We recognize that adding new features or enhancements to any project is a task that needs more recognition. If you want your contribution advertised, we are happy to do so through our webpage. Just let us know and we will add your name, a short description, and links to any publications here.

Contributing with a bug report

Bug reports are a very welcome feedback! These should be posted in the i-PI Github repository (issues tab). Please include inputs and outputs that allow us to reproduce the bug, and a short description of the bug you are encountering.