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First‐Principles Calculation of Electronic, Optical, and Structural Properties of α‐Al 2 O 3
Author(s) -
Ching W. Y.,
Xu YongNian
Publication year - 1994
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1994.tb07008.x
Subject(s) - band gap , electronic structure , local density approximation , chemistry , electronic band structure , density functional theory , direct and indirect band gaps , dielectric , ionic bonding , atomic physics , condensed matter physics , materials science , computational chemistry , physics , ion , optoelectronics , organic chemistry
The electronic structure, the linear optical properties, and the structural properties of α‐Al 2 O 3 in the corundum structure are studied by means of first‐principles local density calculations. An indirect band gap of 6.29 eV is obtained, which is almost the same as the direct band gap of 6.31 eV at Γ. The calculated density of states are compared with X‐ray photoemission and photoabsorption measurements. Real space charge density analysis shows Al, 2 O 3 to be highly ionic with an effective charge formula of Al 2 +2.75 O 3 −1.83 . The calculated dielectric function is in general agreement with the experimental vacuum ultraviolet data. It is shown that the component with c‐direction polarization is in better agreement with the experimental data because it is less affected by the exciton formation near the absorption edge. The intrinsic difference between the calculated local density approximation gap and the measured optical gap is pointed out. Various careful test calculations indicate that the remaining discrepancy in the optical spectra may be in the LDA approximation of the electronic structure theory. The total energy calculation for the ground‐state structural properties of α‐Al 2 O 3 shows excellent agreement with experimental data: the calculated equilibrium volume, c/a ratio, bulk modulus, and internal parameters for Al and O atoms differ from measured values by 0.0, −4.3, −4.0,0.85, and 1.96 percent, respectively. The calculations for the electronic structure and the optical properties are repeated with crystal parameters obtained at 2000°C. The result shows only a slight reduction in the band gap (to 5.76 eV at Γ), with the optical spectra essentially unchanged.