Quasiparticle and Optical Properties of Rutile and Anatase Ti2O2
Quasiparticle excitation energies and optical properties of TiO{sub 2} in the rutile and anatase structures are calculated using many-body perturbation-theory methods. Calculations are performed for a frozen crystal lattice; electron-phonon coupling is not explicitly considered. In the GW method, several approximations are compared and it is found that inclusion of the full frequency dependence as well as explicit treatment of the Ti semicore states are essential for accurate calculation of the quasiparticle energy-band gap. The calculated quasiparticle energies are in good agreement with available photoemission and inverse photoemission experiments. The results of the GW calculations, together with the calculated static screened Coulomb interaction, are utilized in the Bethe-Salpeter equation to calculate the dielectric function {epsilon}{sub 2}({omega}) for both the rutile and anatase structures. The results are in good agreement with experimental observations, particularly the onset of the main absorption features around 4 eV. For comparison to low-temperature optical-absorption measurements that resolve individual excitonic transitions in rutile, the low-lying discrete excitonic energy levels are calculated with electronic screening only. The lowest energy exciton found in the energy gap of rutile has a binding energy of 0.13 eV. In agreement with experiment, it is not dipole allowed but the calculated exciton energy exceeds that measured in absorption experiments by about 0.22 eV and the scale of the exciton binding energy is also too large. The quasiparticle energy alignment of rutile is calculated for nonpolar (110) surfaces. In the GW approximation, the valence-band maximum is 7.8 eV below the vacuum level, showing a small shift from density-functional theory results.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 988811
- Report Number(s):
- BNL-91144-2010-JA; R&D Project: NC-001; KC020401H; TRN: US201018%%678
- Journal Information:
- Physical Review. B. Condensed Matter and Materials Physics, Vol. 82, Issue 8; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ABSORPTION
ALIGNMENT
APPROXIMATIONS
BETHE-SALPETER EQUATION
BINDING ENERGY
CRYSTAL LATTICES
DIELECTRIC MATERIALS
DIPOLES
ELECTRON-PHONON COUPLING
ENERGY GAP
ENERGY LEVELS
EXCITATION
EXCITONS
FREQUENCY DEPENDENCE
OPTICAL PROPERTIES
PERTURBATION THEORY
PHOTOEMISSION
RUTILE
tiO2
electronic excitations
optical excitations
excitons
many-body perturbation theory
functional nanomaterials