Hardness and excitation energy

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The concept of the ensemble Kohn-Sham hardness is introduced. It is shown that the first excitation energy can be given by the Kohn-Sham hardness (i.e. the energy difference of the ground-state lowest unoccupied and highest occupied levels) plus an extra term coming from the partial derivative of the ensemble exchange-correlation energy with respect to the weighting factor w in the limit w→0. It is proposed that the first excitation energy can be used as a reactivity index instead of the hardness.

Original languageEnglish
Pages (from-to)437-440
Number of pages4
JournalJournal of Chemical Sciences
Issue number5
Publication statusPublished - Sep 2005



  • Excitation energy
  • Kohn-Sham hardness
  • Reactivity index

ASJC Scopus subject areas

  • Chemistry(all)

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