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A Comparison Between Hybrid Functional, GW Approach and the Bethe Salpether Equation: Optical Properties of High Pressure Phases of TiO2
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.ORCID iD: 0000-0001-7321-8594
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
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2014 (English)In: Science of Advanced Materials, ISSN 1947-2935, E-ISSN 1947-2943, Vol. 6, no 6, 1170-1178 p.Article in journal (Refereed) Published
Abstract [en]

Titanium dioxide has good corrosion resistance in aqueous solutions and is a good candidate for photoelectrodes. The limitation of the anatase phase of TiO2 is its large band gap. High pressure phases of TiO2 like fluorite, pyrite and cotunnite may possess a more suitable band gap than the well known atmospheric phases. In this paper, the electronic properties of high pressure phases of TuO(2), fluorite, pyrite and cotunnite, have been investigated by hybrid functional and GW methods. Our calculations suggest that the band gap of fluorite and pyrite phases have optimal band gaps to absorb visible light for photocatalysis to decompose water. The imaginary part of the dielectric function has also been calculated for fluorite, pyrite, cotunnite and anatase phases using the Bethe-Salpether (BSE) method. The dielectric function calculated by BSE for the anatase phase agrees well with experiment and with previous studies, using the same level of theory. Therefore we expect that we are also able to predict the optical properties of the high pressure phases of TiO2 by the BSE method. The spatial properties and the localization character of excitons in these high pressure phases were investigated and discussed in terms of photoconversion efficiency.

Place, publisher, year, edition, pages
2014. Vol. 6, no 6, 1170-1178 p.
Keyword [en]
High Pressure, Titanium Dioxide, Hybrid Functional, GW, BSE
National Category
Physical Chemistry
URN: urn:nbn:se:kth:diva-145886DOI: 10.1166/sam.2014.1883ISI: 000337268100012ScopusID: 2-s2.0-84904627960OAI: diva2:720958
Swedish Research Council

QC 20140603

Available from: 2014-06-03 Created: 2014-06-03 Last updated: 2014-08-07Bibliographically approved
In thesis
1. Electronic Structure and Optical Properties of Solar Energy Materials
Open this publication in new window or tab >>Electronic Structure and Optical Properties of Solar Energy Materials
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, we have studied the electronic and optical properties of solar energy m-terials. The studies are performed in the framework of density functional theory (DFT), GW, Bethe-Salpeter equation (BSE) approaches and Kinetic Monte Carlo (KMC). We present four sets of results. In the first part, we report our results on the band gap engineering issues for BiNbO4and NaTaO3, both of which are good photocatalysts. The band gap tuning is required for these materials in order to achieve the maximum solar to hydrogen conversion efficiency. The most common method for the band gap reduction is an introduction of foreign elements. The mono-doping in the system generates electrons or holes states near band edges, which reduce the efficiency of photocatalytic process. Co-doping with anion and cation or anion and anion can provide a clean band gap. We have shown that further band gap reduction can be achieved by double-hole mediated coupling between two anionic dopants. In the second part, the structure and optical properties of (CdSxSe1x)42nanoclusters have been studied. Within this study, the structures of the (CdS)42, (CdSe)42, Cd42Se32S10, Cd42Se22S20, and Cd42Se10S32 clusters have been determined using the simulated annealing method. Factors influencing the band gap value have been analyzed. We show that the gap is most significantly reduced when strongly under coordinated atoms are present on the surface of the nanoclusters. In addition, the band gap depends on the S concentration as well as on the distribution of the S and Se atoms in the clusters. We present the optical absorption spectra calculated with BSE and random phase approximation (RPA) methods based on the GW corrected quasiparticle energies. In the third part, we have employed the state-of-art computational methods to investigate the electronic structure and optical properties of TiO2high pressure polymorphs. GW and BSE methods have been used in these calculations. Our calculations suggest that the band gap of fluorite and pyrite phases have optimal values for the photocatalytic process of decomposing water in the visible light range. In the fourth part we have built a kinetic model of the first water monolayer growth on TiO2(110) using the kinetic Monte Carlo (KMC) method based on parameters describing water diffusion and dissociation obtained from first principle calculations. Our simulations reproduce the experimental trends and rationalize these observations in terms of a competition between different elementary processes. At high temperatures our simulation shows that the structure is well equilibrated, while at lower temperatures adsorbed water molecules are trapped in hydrogen-bonded chains around pairs of hydroxyl groups, causing the observed higher number of molecularly adsorbed species at lower temperature.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. viii, 82 p.
GW, Bethe-Salpeter equation, Kinetic Monte Carlo, Density Functional Theory
National Category
Condensed Matter Physics
Research subject
Materials Science and Engineering
urn:nbn:se:kth:diva-145625 (URN)978-91-7595-190-4 (ISBN)
Public defence
2014-06-13, FB53, AlbaNova, Roslagstullsbacken, Stockholm, 10:00 (English)

QC 20140603

Available from: 2014-06-03 Created: 2014-05-23 Last updated: 2014-06-03Bibliographically approved

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