Electronic Structure of Titanium Oxide Crystal Surface with Lithium Atom on the Surface
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Electronic Structure of Titanium Oxide Crystal Surface with Lithium Atom on the Surface M. Oshikiri, F. Aryasetiawan1 and M. Boero1 Physical Properties Division, National Research Institute for Metals 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan 1 Theory Research Group, Joint Research Center for Atom Technology – Angstrom Technology Partnership 1-1-4 Higashi, Tsukuba, Ibaraki 305-0046, Japan ABSTRACT The electronic structure of the bulk TiO2 in the rutile structure, geometric and electronic structure of two dimensional titanium oxide and lithium titanium oxide layers have been investigated. Not only density functional approach within the local density approximation (LDA) but also GW approach has been tried and the LDA electronic band structures have been compared with the quasiparticle energy structures. The unit cells which include a few atomic layers and open space of more than several angstroms have been used as geometric model of the surface. The surface geometric relaxation has been investigated by the Car-Parrrinello quantum molecular dynamics method based on the plane wave basis with pseudo potential within Becke-Lee-Yang-Parr (BLYP) generalized gradient approximation (GGA) and the quasiparticle energy structure has been obtained by the GW method based on the linearized muffin tin orbital (LMTO) basis with the atomic sphere approximation (ASA). Good applicability of this hybridized first principles approach has been confirmed.
INTRODUCTION Nowadays the titanium oxide and its related materials are on the focus of strong technological interest, for example, a promising photo catalyst [1] and an electrode material of Li ion secondary battery [2]. There is also some scientific interest about superconductivity in the lithium titanium oxide system [3]. There are still many unknown physical properties of the conduction band spanned by the 3d orbital of the titanium. On the other hand, in the previous decade, the quantum molecular dynamics simulation technique, the so called Car-Parrinello method [4-6], has been well established and a first principles method beyond the LDA [7], the so called GW method [8-10], has also been developed. The GW method can remove the self interaction problem [11] in the conventional DFT-LDA and the physical meaning of the GW approach corresponds to the photoemission or inverse photoemission experiment. Then the GW method can predict the band gap in principle. It would be convenient that one regards the GW approximation (GWA) as the Hartree-Fock approximation with a screening effect. It has been already confirmed that our GW method can predict the quasiparticle energy structures of various wide gap s-p system semiconductors in very good agreements with experiments [12]. It is well known that the ZnO system includes the strong hybridization of the 3d orbital of Zn and 2p orbital of oxygen in the valence band. Even in this case, the GW could predict a reasonable electronic structure [12]. The GW can take account the correlation only up to the random phase approximation (RPA), i.e. screen
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