Electron correlation in Sr(Ca)RuO

We have investigated the role of electron-electron correlation in SrRuO3 and CaRuO3 bulk structures. At first, the DOS of SrRuO3 and CaRuO3 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 SrRuO3 and CaRuO3 by GWA. The shifting of the Ru t2g 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 experimental results due to small shifting of the Ru t2g bands and small broadening of the valance states specially in the Ca-based system. Inclusion of Coulomb correlation by LSDA+U for both Sr- and Ca-based compounds shows significant difference in the results as compared with the LSDA and GWA calculations, and is consistent with the PES results. So, the discrepancy between the bulk ab-initio calculation and experiment is attributed to the surface effects which is not considered in the both LSDA and GWA bulk calculations. Due to the more distorted structure of CaRuO3, electron correlation at surface in the Ca-based system is more important than that in the Sr-based system. Hence, the bulk character of both SrRuO3 and CaRuO3 experimental results can be well described by GWA