2008/06/25 by Hector Mera, Mera, Hector
Physics and Astronomy · #FOS: Physical sciences #Other Condensed Matter (cond-mat.other) #cond-mat.other
paper · pdf · doi:10.48550/arxiv.0806.4060
5 pages, 2 tables, 1 figure. Submitted to Phys. Rev. B
arxiv created 2008/06/25 · arxiv updated 2009/12/01
We use projector operators to correct the Kohn-Sham Hamiltonian of density functional theory (KS-DFT) so that the resulting mean-field scheme yields, in finite systems, virtual orbitals and energy gaps in better agreement with those predicted by quasiparticle theory. The proposed correction term is a scissors-like operator of the form (I-ρ)δH(I-ρ), where I is the identity operator, ρ the density matrix of the N-particle system and δH is either the difference between the N+1- and N-particle Kohn-Sham Hamiltonians or a non-self-consistent approximation to it. Such a term replaces the Kohn-Sham virtual orbitals of the N-particle system by the HOMO and virtual orbitals of the system with N+1 particles in an attempt to mimic a true quasiparticle spectrum. Using a local density approximation (LDA) we compute the gaps of a variety of small molecules finding good agreement with experiment and computationally more demanding methods. For these systems we examine the physical origin of this gap correction and show that so-called band gap discontinuity, Δxc, contains electrostatic contributions that do not originate from the discontinuity in the exchange-correlation potential. The similarity between the corrected and Hartree-Fock virtual orbitals is illustrated and the extent to which the bare LDA virtual orbitals are improved is considered. The lack of band-gap discontinuity and the presence of self-interaction errors in the proposed correction are also discussed.