First-principles calculation of electric field gradients at the Cu sites in YBa2Cu3O7

First-principles calculation of electric field gradients and hyperfine couplings in YBa2Cu3O7

“…The experimental values for the quadrupole resonance frequencies [26] have been converted into EFGs using the value of Q( 63 Cu) = −0.211 b for the nuclear quadrupole moment [27]. Also given in Table 4 are previous theoretical values obtained from band structure calculations [12,14] and from a spin non-polarized cluster calculation [16]. The present results are in good agreement with the experimental data.…”

“…A comparison of the theoretical results with experimental values shows that the new spin-polarized calculations here are distinctly better than our previous spinunpolarized calculations [16] and the FLAPW calculations [12,14]. The FLAPW values are only about 50% of the experimental values although the contributions from the 3p and 3d orbitals (with the exception of the 3d x 2 −y 2 orbital) are almost identical with our current calculations.…”

“…In any case, as earlier work has shown [17], there is no significant change if the quality of this basis set is improved. Pseudopotentials were used [20] In contrast to our previous work [16] on YBa 2 Cu 3 O 7 we present here spin polarized calculations using the Gaussian 98 software package [19].…”

Cluster Calculations of Electric-Field-Gradients at the Ta Site for the Ferroelectric LiTaO 3 Crystal

“…The two last approaches have an advantage over the first one because they include directly core polarization, valence electron, and bonding effects and do not need in introducing the antishielding parameters. Theoretical calculations made with these first-principles methods usually give a good agreement with experiments (see [11] and references therein). As it is shown below, the main contribution to EFG at the Ta site in the LiTaO 3 crystal arises due to nearest oxygen ions.…”

“…The second and more correct approach to EFG calculations in crystals is based on the band structure models such as the LAPW (linearizedaugmented-plane-wave) method [8,9]. When the EFG tensor at nucleus sites is mainly determined by the nearest neighbourhood, the ab initio cluster MO LCAO SCF (molecular-orbitals-linear-combination-of-atomic-orbitals selfconsistent field) approach can be used (see, for example, [10][11][12]). The two last approaches have an advantage over the first one because they include directly core polarization, valence electron, and bonding effects and do not need in introducing the antishielding parameters.…”