title: Assessment of Tuning Methods for Enforcing Approximate Energy Linearity in Range-Separated Hybrid Functionals.
abstract: A range of tuning methods, for enforcing approximate energy linearity through a system-by-system optimization of a range-separated hybrid functional, are assessed. For a series of atoms, the accuracy of the frontier orbital energies, ionization potentials, electron affinities, and orbital energy gaps is quantified, and particular attention is paid to the extent to which approximate energy linearity is actually achieved. The tuning methods can yield significantly improved orbital energies and orbital energy gaps, compared to those from conventional functionals. For systems with integer M electrons, optimal results are obtained using a tuning norm based on the highest occupied orbital energy of the M and M + 1 electron systems, with deviations of just 0.1-0.2 eV in these quantities, compared to exact values. However, detailed examination for the carbon atom illustrates a subtle cancellation between errors arising from nonlinearity and errors in the computed ionization potentials and electron affinities used in the tuning.
authors.affiliation: Department of Chemistry, Durham University , South Road, Durham, DH1 3LE, United Kingdom.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Gledhill
authors.affiliation: Department of Chemistry, Faraday Building, Lancaster University , Lancaster, LA1 4YB, United Kingdom.
authors.forename: Michael J G
authors.initials: MJ
authors.lastname: Peach
authors.affiliation: Department of Chemistry, Durham University , South Road, Durham, DH1 3LE, United Kingdom.
authors.forename: David J
authors.initials: DJ
authors.lastname: Tozer