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Electric field gradients in cuprates: Does LDA+U give the correct charge distribution?
Author(s) -
Blaha P.,
Schwarz K.,
Novák P.
Publication year - 2004
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.20310
Subject(s) - antiferromagnetism , condensed matter physics , cuprate , superconductivity , electric field gradient , spin (aerodynamics) , ground state , charge (physics) , chemistry , physics , electric field , atomic physics , quantum mechanics , thermodynamics
We present calculations for the electric field gradients (EFG) on the Cu sites in La 2 CuO 4 , YBa 2 Cu 3 O 6 , and YBa 2 Cu 3 O 7 using standard LDA and GGA exchange‐correlation functionals, but also by using the LDA+U method for the correlated Cu‐d electrons. LDA or GGA calculations yield proper EFGs in agreement with experiment for all sites except the planar Cu(2) site, where the theoretical EFGs are too small by a factor of 2 to 3. This happens for both the metallic (superconducting) YBa 2 Cu 3 O 7 and the antiferromagnetic insulators. For the latter, these calculations also lead to a nonmagnetic and metallic solution. Application of LDA+U with various double‐counting corrections and varying values for the Hubbard parameter U gives the correct magnetic and insulating ground state and the corresponding EFGs are substantially enhanced. Best agreement with experiment is found using the LDA+U(FLL) method with U around 6 eV, because this method leaves the Cu(1) EFG unchanged, even when U is applied to its d ‐states. For the metallic compound YBa 2 Cu 3 O 7 , the EFG results favor the presence of local magnetic moments; however, in bandstructure calculations the necessary long‐range order leads to some artifacts and should be replaced by random spin fluctuations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005