Journal Article conceptual density functional theory dual descriptor Conceptual Density-Functional Theory Research Support, Non-U.S. Gov't all-metal clusters aromaticity boron clusters cyclic electron delocalization degeneracy in frontier molecular orbitals density polarization electronic densities electrophilic Fukui function linear response function local hyper-softness local peripheral reactivity local reactivity mesomeric effect metal-organic Mo-oxo complexes molecular electrostatic potential nucleophilic Fukui function substituent effect symmetric molecules total electronic densities