Koopmans' springs to life

Ulrike Salzner*, Roi Baer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

182 Scopus citations

Abstract

The meaning of orbital energies (OOEs) in Kohn-Sham (KS) density functional theory (DFT) is subject to a longstanding controversy. In local, semilocal, and hybrid density functionals (DFs) a Koopmans' approach, where OOEs approximate negative ionization potentials (IPs), is unreliable. We discuss a methodology based on the Baer-Neuhauser-Livshits range-separated hybrid DFs for which Koopmans' approach "springs to life." The OOEs are remarkably close to the negative IPs with typical deviances of ±0.3 eV down to IPs of 30 eV, as demonstrated on several molecules. An essential component is the ab initio motivated range-parameter tuning procedure, forcing the highest OOE to be exactly equal to the negative first IP. We develop a theory for the curvature of the energy as a function of fractional occupation numbers to explain some of the results.

Original languageAmerican English
Article number231101
JournalJournal of Chemical Physics
Volume131
Issue number23
DOIs
StatePublished - 2009

Bibliographical note

Funding Information:
This work was supported by the European Union 7, framework project Unam-Regpot (Contract 203953) and TŰBITAK (Contract 109T426), the Bilkent University, and by the Israel Science Foundation (Contract 962/06).

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