... it as follows:
Gunter Hermann, Vincent Pohl, Jean Christophe Tremblay, Beate Paulus, Hans-Christian Hege, and Axel Schild, "ORBKIT: A Modular Python Toolbox for Cross-Platform Postprocessing of Quantum Chemical Wavefunction Data", J. Comput. Chem. 2016, DOI: 10.1002/jcc.24358.
orbkit's documentation can be found at http://orbkit.github.io/