v2.2.1

This release is described in the following published paper:

Extension of the QuickFF force field protocol for an improved accuracy of structural, vibrational, mechanical and thermal properties of Metal Organic Frameworks, L. Vanduyfhuys, S. Vandenbrande, J. Wieme, M. Waroquier, T. Verstraelen, V. Van Speybroeck, Journal of Computational Chemistry
http://dx.doi.org/10.1002/jcc.25173