Ag Raman modes of RBCO (R = Gd, Pr) by density functional theory approach
Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365, Tehran, Iran
Corresponding author: a email@example.com
Revised: 22 March 2006
Published online: 2 June 2006
Ab initio total energy calculations have been performed for superconducting GdBa2Cu3O7 and insulating PrBa2Cu3O7 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 the two systems in equilibrium structure have been obtained in GGA. The calculated frequencies in the GGA are in good agreement with the other LDA calculations for similar systems. Comparison of computational data with experimental data indicates that calculations determine the frequencies about ten percent below the experimental data. Even by improving LDA to GGA in these calculations, the calculated phonon frequencies have remained almost ten percent below the experimental data, even though the calculated unit cell volumes are nearly equal to the experimental data. So, applying GGA has not considerably decreased the difference between the computational and experimental data. The effect of Pr doping on the eigenvalues and eigenvectors have also been investigated.
PACS: 74.25.Kc – Phonons / 31.15.Ew – Density-functional theory / 33.20.Fb – Raman and Rayleigh spectra (including optical scattering) / 74.72.Bk – Y-based cuprates
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2006