A library of approximate exchange-correlation functionals
XCFun is a library of approximate exchange-correlation functionals, used in the Density Functional Theory description of electronic structure. Because XCFun is based on automatic differentiation the library can provide arbitrary order derivatives of all supported functionals. Only the exchange-correlation energy expression needs to be implemented, which is a huge gain in productivity (and also efficiency). For this reason the library is very well suited for high order time dependent DFT or for the development of new functionals.