Steven Feldgus Clark R. Landis Eric D. Glendening Frank Weinhold Natural resonance theory. I. General formalism. 411-413 2000 21 Journal of Computational Chemistry 5 http://dx.doi.org/10.1002/(SICI)1096-987X(20000415)21:5<411::AID-JCC7>3.0.CO;2-4 db/journals/jcc/jcc21.html#FeldgusLGW00