Libxc is a library of exchange-correlation and kinetic energy functionals for density-functional theory. Its aim is to provide a portable, well tested and reliable set of these functionals in line with the modular paradigm of software development. The library currently implements over 600 density functional approximations, and is used by over 30 electronic structure programs ranging from atomic structure calculations to large quantum chemistry and materials modeling programs. New density functionals need only be added to Libxc to become available in any program that relies on Libxc for density functional calculations. Having access to the exact same implementation across programs also enables apples-to-apples comparisons between various numerical approaches.

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