Spin-state splittings, highest-occupied-molecular-orbital and lowest-unoccupied-molecular-orbital energies, and chemical hardness
Abstract
It is known that the exact density functional must give ground-state energies that are piecewise linear as a function of electron number. In this work we prove that this is also true for the lowest-energy excited states of different spin or spatial symmetry. This has three important consequences for chemical applications: the ground state of a molecule must correspond to the state with the maximum highest-occupied-molecular-orbital energy, minimum lowest-unoccupied-molecular-orbital energy, and maximum chemical hardness. The beryllium, carbon, and vanadium atoms, as well as the CH2 and C3H3 molecules are considered as illustrative examples. Our result also directly and rigorously connects the ionization potential and electron affinity to the stability of spin states.
- Publication:
-
Journal of Chemical Physics
- Pub Date:
- October 2010
- DOI:
- Bibcode:
- 2010JChPh.133p4107J
- Keywords:
-
- beryllium;
- carbon;
- density functional theory;
- electron affinity;
- excited states;
- ground states;
- ionisation potential;
- organic compounds;
- 31.15.E-;
- 32.10.Hq;
- 33.15.Ry;
- Density-functional theory;
- Ionization potentials electron affinities;
- Ionization potentials electron affinities molecular core binding energy