Improved quasiparticle wave functions and mean field for G0W0 calculations: Initialization with the COHSEX operator

Manish Jain, Jack Deslippe, Georgy Samsonidze, Marvin L. Cohen, James R. Chelikowsky, and Steven G. Louie
Phys. Rev. B 90, 115148 – Published 26 September 2014

Abstract

The GW approximation to the electron self-energy has become a standard method for ab initio calculation of excited-state properties of condensed-matter systems. In many calculations, the GW self-energy operator, Σ, is taken to be diagonal in the density functional theory (DFT) Kohn-Sham basis within the G0W0 scheme. However, there are known situations in which this diagonal G0W0 approximation starting from DFT is inadequate. We present two schemes to resolve such problems. The first, which we called scCOHSEX+GW, involves construction of an improved mean field using the static limit of GW, known as COHSEX (Coulomb hole and screened exchange), which is significantly simpler to treat than GW. In this scheme, frequency-dependent self energy Σ(ω), is constructed and taken to be diagonal in the COHSEX orbitals after the system is solved self-consistently within this formalism. The second method is called off diagonal-COHSEX GW (odCOHSEX+GW). In this method, one does not self-consistently change the mean-field starting point but diagonalizes the COHSEX Hamiltonian within the Kohn-Sham basis to obtain quasiparticle wave functions and uses the resulting orbitals to construct the GW Σ in the diagonal form. We apply both methods to a molecular system, silane, and to two bulk systems, Si and Ge under pressure. For silane, both methods give good quasiparticle wave functions and energies. Both methods give good band gaps for bulk silicon and maintain good agreement with experiment. Further, the scCOHSEX+GW method solves the qualitatively incorrect DFT mean-field starting point (having a band overlap) in bulk Ge under pressure.

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  • Received 11 September 2013
  • Revised 25 July 2014

DOI:https://doi.org/10.1103/PhysRevB.90.115148

©2014 American Physical Society

Authors & Affiliations

Manish Jain1,2,3,4, Jack Deslippe2,3,5, Georgy Samsonidze2,3,*, Marvin L. Cohen2,3, James R. Chelikowsky1,6, and Steven G. Louie2,3

  • 1Center for Computational Materials, Institute for Computational Engineering and Sciences, University of Texas, Austin, Texas 78712, USA
  • 2Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA
  • 3Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
  • 4Department of Physics, Indian Institute of Science, Bangalore 560 012, India
  • 5NERSC, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
  • 6Departments of Physics and Chemical Engineering, University of Texas, Austin, Texas 78712, USA

  • *Present address: Research and Technology Center, Robert Bosch LLC, Cambridge, MA 02142, USA.

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Issue

Vol. 90, Iss. 11 — 15 September 2014

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