Spin-state splittings, highest-occupied-molecular-orbital and lowest-unoccupied-molecular-orbital energies, and chemical hardness.

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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 CH(2) and C(3)H(3) 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.






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Johnson, Erin R, Weitao Yang and Ernest R Davidson (2010). Spin-state splittings, highest-occupied-molecular-orbital and lowest-unoccupied-molecular-orbital energies, and chemical hardness. J Chem Phys, 133(16). p. 164107. 10.1063/1.3497190 Retrieved from https://hdl.handle.net/10161/3345.

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Weitao Yang

Philip Handler Distinguished Professor of Chemistry

Prof. Yang, the Philip Handler Professor of Chemistry, is developing methods for quantum mechanical calculations of large systems and carrying out quantum mechanical simulations of biological systems and nanostructures. His group has developed the linear scaling methods for electronic structure calculations and more recently the QM/MM methods for simulations of chemical reactions in enzymes.

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