Valence Virtual Orbitals: An Unambiguous ab Initio Quantification of the LUMO Concept Schmidt, Michael W. ; Hull, Emily A. ; Windus, Theresa L. Abstract Publication: Journal of Physical Chemistry A Pub Date: October 2015 DOI: 10.1021/acs.jpca.5b06893 Bibcode: 2015JPCA..11910408S