Structure, electronic, and optical properties of TiO2 atomic clusters: An ab initio study

Abstract

Atomic clusters of TiO(2) are modeled by means of state-of-the-art techniques to characterize their structural, electronic and optical properties. We combine ab initio molecular dynamics, static density functional theory, time-dependent density functional theory, and many body techniques, to provide a deep and comprehensive characterization of these systems. TiO(2) clusters can be considered as the starting seeds for the synthesis of larger nanostructures, which are of technological interest in photocatalysis and photovoltaics. In this work, we prove that clusters with anatase symmetry are energetically stable and can be considered as the starting seeds to growth much larger and complex nanostructures. The electronic gap of these inorganic molecules is investigated, and shown to be larger than the optical gap by almost 4 eV. Therefore, strong excitonic effects appear in these systems, much more than in the corresponding bulk phase. Moreover, the use of various levels of theory demonstrates that charge transfer effects play an important role under photon absorption, and therefore the use of adiabatic functionals in time dependent density functional theory has to be carefully evaluated.

Electronic and Optical Properties of Oxides Nanostructures by First-Principles Approaches

“…The largest KS gap (2.8 eV) is obtained for the (TiO 2 ) 8 system, which is the only cluster with a gap larger than the bulk anatase DFT value. The electronic gap, calculated as E gap DFT (within DSCF, as IP-EA, with (IP) ionization potential and Encyclopedia of Nanotechnology DOI 10.1007/978-94-007-6178-0_100933-1 # Springer Science+Business Media Dordrecht 2015 (EA) electron affinity) or via G 0 W 0 , has quite large values (in the range 4.5-7.0 eV), due to the strong quantum confinement of these atomic-size systems, and shows a quite good agreement with experimental data [30]. Because of the strong many-body effects, the electronic gaps of these inorganic molecules are also several eV (about 4 eV) larger of the Kohn-Sham [39] and optical gaps (Fig.…”

“…1). This is not surprising, as in localized systems the strong electron-hole interaction induces bound excitonic states, with e-hbinding energies much larger than in the bulk phase [30,31,40]. Indeed optical spectra of the smallest clusters, calculated at the many-body level, including the electron-hole interaction (i.e., by solving the BSE equation [6]), show a strong red shift from electronic to optical gap, with BSE gap larger than the KS-PBE gap and quite close to KS-PBE0 values [30].…”

“…As applications of first-principles GS and excited state methods to the class of oxide nanostructures, two examples are discussed in the following: zero-dimensional atomic clusters [30,31] and two-dimensional nanosheets [32] of titanium dioxide.…”

Titanium Dioxide Nanomaterials: Self-Structural Modifications

“…193 Chiodo et al simulated atomic clusters of TiO 2 by ab initio molecular dynamics (MD), DFT, TDDFT, and many-body techniques and suggested that clusters with anatase symmetry were energetically stable and could be considered as the starting seeds to grow much larger and more complex nanostructures. 194 They found that the electronic gap of these inorganic molecules was larger than the optical gap by almost 4 eV with strong excitonic effects and that charge-transfer effects played an important role under photon absorption. 194 Guisbiers et al studied the change of melting temperature and band gap of TiO 2 nanomaterials caused by the size.…”

Ab-initio study of free standing TiO2 clusters: Stability and magnetism

“…[12][13][14] A wide plethora of reported studies already exist on the spectroscopic analysis of TiO 2 metal dioxide clusters giving information about the structure and bonding in clusters. 15 It is being addressed the electronic structure information about (TiO 2 ) n clusters with n ¼ 1-10 using photoelectron spectroscopy (PES) and the magnetism for anatase phase clusters has been observed experimentally by Wei et al 16 Chiodo et al 17 and Mo et al 18 have studied the electronic, structural, and optical properties of titanium dioxide clusters employing ab-initio calculations. Relative stability of (TiO 2 ) n cluster for different symmetries was studied by Albaret et al using Density Functional Theory (DFT).…”