Calculations of Atomic and Electronic Structure for (100) Surfaces of SrTiO 3 Perovskite
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Calculations of Atomic and Electronic Structure for (100) Surfaces of SrTiO3 Perovskite
R. I. Eglitisa, E. Heifetsb, E. A. Kotominc, and G. Borstela a Department of Physics, University of Osnabrueck, D-49069 Osnabrueck, Germany b California Institute of Technology, Ms 139-74, Pasadena CA 91125, USA c Institute of Solid State Physics, University of Latvia, 8 Kengaraga str., Riga LV-1063, Latvia ABSTRACT We present and discuss main results of the calculations for the surface relaxation and rumpling of SrTiO3 surfaces with TiO2 and SrO terminations using a wide variety of methods of modern computational physics and chemistry, including the shell model (SM) and ab initio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT). The HF and DFT formalisms with different exchange-correlation functionals are implemented into Crystal-98 computer code using a Gaussian-type basis set. We demonstrate that a hybrid B3PW formalism gives the best results for the bulk SrTiO3 properties. Results are compared with previous ab initio plane-wave LDA calculations and LEED experiments. Our calculations demonstrate an increase of the covalency effects between Ti and O atoms near the surface. INTRODUCTION Thin films of perovskite ferroelectrics are important for many technological applications, where surface structure and its quality are of primary importance [1-4]. In this paper, we calculated the relaxed atomic structure of the SrTiO3 surface in the cubic phase. The SrTiO3 (100) surface relaxation has been experimentally studied by means of several techniques, e.g. low energy electron diffraction (LEED), reflection high-energy electron diffraction (RHEED), medium energy ion scattering (MEIS) and surface X-ray diffraction (SXRD) measurements [5-9]. Several ab initio [10-17] and shell model (SM) [18,19] theoretical studies were published recently for the (100) surface of BaTiO3 and SrTiO3 crystals. In order to study dependence of the surface relaxation properties on exchange-correlation functionals and localized/plane wave basis sets used in our calculations, in this paper we performed a detailed comparative study based on a number of different techniques. Preliminary results are published in Ref. [20]. METHOD In this study we restrict ourselves to simulations of SrTiO3 in the cubic perovskite phase, with (001) surfaces terminated by a plane containing SrO or TiO2 units. To simulate both surfaces, we used symmetrical slabs consisting of seven alternating TiO2 and SrO layers. The total energies and electronic structures of these slabs were calculated by several quite different methods: HF with different DFT-type a posteriori electron correlation corrections to the total energy [21] such as Generalized Gradient Approximation (HFGGA), Perdew-91
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(HFPer91), Lee-Yang-Parr (HFLY
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