Theory of63Cu and17O quadrupole interactions in copper oxide high-T c systems

Electronic structure of ceramics at the MP2 electron correlation level

“…In this paper, we attempt to fill this gap, and present the results of cluster electronic structure calculations at the UHF and the Møller-Plesset levels for YBa 2 Cu 3 O 7 ceramics with a self-consistent account taken of the infinite-crystal surroundings of the quantum cluster; these calculations, where the lattice is considered as a static lattice, correspond to overdoped ceramics. The Gaussian basis set employed is larger than those used in previous cluster calculations [15,19,21,28]. The results obtained in this study reveal the strong influence of the electron correlation effect on the charge distribution and the orbital population of Cu and O atoms.…”

“…The charges of the outermost ions are adjusted in order to provide the correct value of the Madelung potential at each cluster site as well as the electrical neutrality of the set: cluster plus background charges. This is achieved by using a procedure originally proposed by Kelires and Das [44,21]. To a shell of n i equal exterior charges q i which creates at the site j a potential V i (j ) is associated a charge scaling factor f i such that the Madelung potential at the site j due to the infinite crystal, V M (j ), is equal to the potential of each shell of scaled charges plus that created by the whole set of charges minus those included in the shells, denoted as V q (j ).…”

“…The electronic structures of the HTSC ceramics have been studied by a variety of methods (see Pickett's review [9] and references ), which range from the band approach (the first publications were by Mattheiss [10] and Freeman with collaborators [11]) to the embeddedcluster method (ECM) [15,19,21,[24][25][26][27][28]. It is well known that the effects of the unusually strong localization in oxides of transition metals make the task of performing electronic structure calculations very difficult [31].…”

“…Such calculations with a precise self-consistent account taken of the crystal surroundings were performed by-at least-four scientific groups: Baetzold [15], Das with co-workers [21,22], Winter et al [27] and Ladik with co-workers [28]. Winter et al [27] performed cluster calculations by the restricted Hartree-Fock (RHF) method, so they did not take into account the electron correlation.…”

On the distribution of intrinsic holes in cuprates

“…There is a multi-pronged attack from both the experimentalist and theorist which are not always cooperative. The theoretical methods, which investigate the electronic structure of these materials, range from band structure [1,2] and supercell approaches which account for dopants [3,4] to cluster calculations [5][6][7][8][9][10][11], but are largely complementary in their areas of success.…”