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SUMMARY:Towards automated self-correction of approximate DFT using first-p
 rinciples Hubbard U and Hund's J parameters - David O’Regan\, School of 
 Physics\, CRANN and AMBER\, Trinity College Dublin\, The University of Dub
 lin\, Dublin 2\, Ireland
DTSTART:20190906T131500Z
DTEND:20190906T141500Z
UID:TALK129277@talks.cam.ac.uk
CONTACT:Angela Harper
DESCRIPTION:In electronic structure methods based on the correction of app
 roximate density-functional theory (DFT) for systematic inaccuracies\, Hub
 bard U parameters may be used to quantify and amend the self-interaction e
 rror (SIE) ascribed to selected subspaces. In order to enable the accurate
 \, computationally convenient calculation of U by means of DFT algorithms 
 that locate the ground-state without any diagonalisation\, such as in line
 ar-scaling DFT+U [1]\, a linear-response formulation for U is introduced h
 ere in terms of the fully-relaxed constrained ground-state density [2]. Ex
 pressing the total energy of self-consistent DFT+U in terms of a constrain
 ed search over ground-state densities and external DFT+U parameters that s
 atisfy a self-consistency condition\, the U parameters are relegated to th
 e status of auxiliary variables. This enables the full comparability\, con
 ceptually and numerically\, of approximately self-corrected DFT energies [
 3\,4]\, such as when external parameters such as ionic positions are chang
 ed.\n\nThis ground-state tracking linear-response framework also addresses
  the open question of self-consistency over U in DFT+U. We show that the s
 implest self-consistency scheme is necessary and sufficient for DFT+U to c
 orrect the total energy for SIE under idealized one-electron conditions [3
 ]\, and that the gap can also be simultaneously corrected if further gener
 alisations are made [4]. For multi-electron systems such as transition-met
 al oxides (including closed-shell ones)\, we extend the framework to enabl
 e straightforward first-principles calculations of the Hund’s exchange p
 arameter J\, which we find to be critically important [5]. We also demonst
 rate successful first-principles U and J corrections for oxygen 2p orbital
 s.\n\n[1] D. D. O’Regan\, N. D. M. Hine\, M. C. Payne\, and A. A. Mostof
 i\, Phys. Rev. B 85\, 085107 (2012). \n\n[2] D. D. O’Regan and G. Teobal
 di\, Phys. Rev. B 94\, 035159 (2016). \n\n[3] G. Moynihan\, G. Teobaldi\, 
 and D. D. O’Regan\, arXiv:1704.08076 (2017).\n\n[4] G. Moynihan\, G. Teo
 baldi\, and D. D. O’Regan\, Phys. Rev. B 94\, 220104(R) (2016). \n\n[5] 
 E. B. Linscott\, D. J. Cole\, M. C. Payne and D. D. O’Regan\, Phys. Rev.
  B 98\, 235157 (2018).\n\n
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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