Sharif Digital Repository

Ab initio total energy calculations have been performed for superconducting GdBa2Cu3O7 and insulating PrBa 2Cu3O7 using the full-potential linear augmented plane-wave method in the local density approximation (LDA) and generalized gradient approximation (GGA). The comparison of the calculated unit cell volume and lattice parameters with the experimental data indicates the improvement of these parameters in the GGA relative to LDA. LDA and GGA give the equilibrium unit cell volume about 6% smaller and 1.25% larger than the experimental data, respectively for both systems. Thus frozen phonon calculations have been performed to determine the eigenvalues and eigenvectors of the k=0 Ag modes of... 

We have investigated the role of electron-electron correlation in SrRuO 3 and CaRuO 3 bulk structures. At first, the DOS of SrRuO 3 and CaRuO 3 is obtained using the full potential linearized augmented plane wave method by LSDA. We have then calculated the electronic structure, dielectric function, self-energy, and spectral function for the bulk SrRuO 3 and CaRuO 3 by GWA. The shifting of the Ru t 2g orbitals, broadening in Ru valance bands, and also the enhancement in exchange splitting shows better agreement between the GWA many-body correction with the bulk experimental results. But, in spite of the many-body correction, the GWA results is not completely consistent with the PES... 

We have calculated the electronic structure of SrRu1-xMn xO3 using the full potential linearized augmented plane wave method by LSDA and LSDAU. The antiparallel alignment between the Mn and Ru ions are consistent with the competition between ferromagnetism and antiferromagnetism in the low Mn-doped polycrystalline samples. This is in contrast to the appearance of quantum critical point and FM and AFM transitions in the single crystal measurement. Our results show that the discrepancy between different experimental phase diagrams is related to the conditions of sample preparation and also the difference between the degree of magnetic interactions between the Mn and Ru moments. The DOS and the... 

We have investigated the electronic structure of Sr(Ca)Ru1-xCrxO3 using the full potential linearized augmented plane wave method by different approximation such as LSDA and LSDA+U. The LSDA calculation suggest that Cr4+-Ru4+ hybridization is responsible for the high Curie temperature TC in SrRu1-xCrxO3, but it cannot completely describe its physical behavior. Our LSDA+U DOS results for SrRu1-xCrxO3 clearly establishes renormalization of the intra-atomic exchange strength at the Ru sites, arising from the Cr-Ru hybridization. The antiferromagnetic coupling of Cr3+ with Ru4+,5+ lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The more distorted...