Capacitance, the Next of Kin to Chemical Softness and Density of States, an Unexpected Perk of Being the “Middle Child”

The capacitance characterizes abilities of various systems to store energy in the form of energy density of electric field. The spatial distribution of electrons exhibits a nonuniform relationship with external potential of atomic nuclei as a consequence of shielding or bonding, and other localized or delocalized charges. Respectively, the stored system energy is affected through thermodynamic displacement. Considering the general resemblance of capacitance definition with two other physical quantities used in the field of chemical physics, the chemical softness or the density of states, it is important to uniquely express this function in nanoscale materials to characterize phenomena resulting from confinement of few electrons generally characterized by density distribution. The exact fundamental linkages and differences between these functions have to be recognized to deal with unintuitive quantum mechanical effects related to the design, development, and comprehending the working principle of nanoscale materials and devices. The locally defined self-capacitance in atomic resolution systems is addressed here to draw the essential links between reactivity and physically observed properties resulting from the energy dispersion or entropy effects in molecular materials