Ag Raman modes of RBCO (R = Gd, Pr) by density functional theory approach |
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Authors: | H Khosroabadi A Tavana M Akhavan |
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Institution: | (1) Department of Physics, Sharif University of Technology, Magnet Research Laboratory (MRL), P.O. Box 11365, Tehran, Iran |
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Abstract: | 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. |
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Keywords: | 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 |
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