Search results for "ODS"
showing 10 items of 5812 documents
Efficient Analysis of Arbitrarily Shaped Inductive Obstacles in Rectangular Waveguides Using a Surface Integral Equation Formulation
2007
In this paper we propose to use the Surface Integral Equation technique for the analysis of arbitrarily shaped Hplane obstacles in rectangular waveguides, which can contain both metallic and/or dielectric objects. The Green functions are formulated using both spectral and spatial images series, whose convergence behavior has been improved through several acceleration techniques. Proceeding in this way, the convergence of the series is not attached to the employment of any particular basis or test function, thus consequently increasing the flexibility of the implemented technique. In order to test the accuracy and numerical efficiency of the proposed method, results for practical microwave c…
Ab Initio Calculations of Hydroxyl Impurities in CaF2
2012
OH– in CaF2 crystal and the (111) surface have been studied by using density functional theory (DFT) with hybrid exchange potentials, namely, DFT-B3PW. Three bulk and 20 surface OH– configurations ...
Ab Initio Calculations of SrTiO3 (111) Surfaces
2012
The paper presents the results of calculations of SrTiO3 polar (111) surface relaxations and energetics using the ab initio code CRYSTAL and a hybrid description of exchange and correlation. Using a hybrid B3LYP approach, the surface relaxation has been calculated for the two possible Ti and SrO3 SrTiO3 (111) surface terminations. For both Ti and SrO3-terminated SrTiO3 (111) surfaces upper layer atoms, with the sole exception of SrO3-terminated surface Sr atom, relax inwards. The calculated surface relaxation energy for Ti-terminated SrTiO3 (111) surface is almost five times larger, than the surface relaxation energy for SrO3-terminated SrTiO3 (111) surface. The surface energy for Ti-termin…
Theoretical Modelling of the Energy Surface (001) and Topology of CaZrO3 Perovskite
2015
I present the results of ab initio calculations of surface relaxations, rumplings, energetics, optical band gaps, and charge distribution for the CaZrO3 (001) surfaces using computer code CRYSTAL and a hybrid description of exchange and correlation. I consider both CaO and ZrO2-terminations of the CaZrO3 (001) surface. On the both CaO and ZrO2-terminated CaZrO3 (001) surfaces, I find that all upper and third layer atoms relax inwards, whereas all second layer atoms relax upwards. I predict a considerable increase of the Zr-O chemical bond covalency (0.102e) near the ZrO2-terminated CaZrO3 (001) surface relative to the CaZrO3 bulk (0.086e). My calculated CaO (0.87 eV) and ZrO2-terminated (1.…
Ab initio Calculations of Bulk and (001) Surface F-centers in ABO3 Perovskites
2021
We analyzed systematic trends in BaTiO 3, SrTiO 3 , PbZrO 3 and SrZrO 3 bulk as well as very rarely performed (001) surface F-center ab initio calculations. The nearest neighbor atomic displacements around the bulk F-center in the ABO 3 perovskites are considerably smaller than the relevant neighbor atomic displacements around the (001) surface $F$ -centers. The $F$ -center electrons are more delocalized for the ABO 3 perovskite (001) surface $F$ -center than for the bulk $F$ -center. Our calculated formation energy differences between the BaTiO 3 , SrTiO 3 , PbZrO 3 and SrZrO 3 bulk and its (001) surface $F$ -centers triggers the $F$ -center segregation from the bulk crystal towards the AB…
Calculations of Surface Structure for SrTiO3 Perovskite
2001
ABSTRACTWe present and discuss results of the calculations for SrTiO3 (100) surface relaxation with different terminations (SrO and TiO2) using a semi-empirical shell model (SM) as well as abinitio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT) formalisms. Using the SM, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized. This permits us determination of surface rumpling and surfaceinduced dipole moments (polarization) for different terminations. We also compare results of the ab initio calculations based on both HF with the DFT-type electroncorrelation corrections, several DFT with different exchange-correlation functional…
Metal clusters on an inert surface: A simple model
1997
The shapes of metal clusters (with 2 to 14 valence electrons) on an inert surface are studied with a simple model based on the ultimate jellium model. It is shown that within certain approximations the surface-cluster interaction can be described with an external potential in the Kohn-Sham method. No restrictions for the cluster geometry are imposed. The results show that depending on the strength of the interaction and on the size of the cluster, the ground state is either planar or three-dimensional, but in many cases both geometries are stable and there is a marked energy barrier between them. The results agree qualitatively with ab initio calculations of Na clusters on a NaCl(100) surfa…
Ab InitioCalculations of the Atomic and Electronic Structure of SrZrO3(111) Surfaces
2012
The paper presents and discusses the results of calculations of surface relaxations and energetics for the polar (111) surface of SrZrO3 using a hybrid B3LYP description of exchange and correlation. On the (111) surface, I consider both Zr- and SrO3-terminations. For both Zr and SrO3-terminated SrZrO3 (111) surfaces upper layer atoms relax inwards. The second layer atoms, with the sole exception of Zr-terminated SrZrO3 (111) surface Sr atom, relax outwards. The calculated surface relaxation energy for Zr-terminated SrZrO3 (111) surface is almost sixteen times larger, than the surface relaxation energy for SrO3-terminated SrZrO3 (111) surface. The surface energy for Zr-terminated SrZrO3 (111…
First-Principles Calculations of SrZrO3 (001) Surfaces
2011
The results of calculations of surface relaxations, rumplings, and charge distribution for the SrZrO3 (001) surface using ab initio code CRYSTAL and a hybrid description of exchange and correlation are presented. Both SrO and ZrO2 terminations of the SrZrO3 (001) surface are considered. On the (001) surfaces all upper and third layer atoms relax inward, while outward relaxations of all atoms in the second layer are found with the sole exception of SrO-terminated SrZrO3 (001) surface second layer O atom. Calculated surface rumpling for the SrO-terminated SrZrO3 (001) surface 6.77% of the lattice constant is by a factor of ten larger than the surface rumpling for the ZrO2-terminated SrZrO3 (0…
Ab initiocalculations of theSrTiO3(110) polar surface
2004
Results of ab initio Hartree-Fock calculations for the SrTiO3 ~110! polar surface are discussed. We have calculated the surface energies, near-surface atomic displacements for four possible terminations ~TiO, Sr, and two kinds of O terminations! as well as Mulliken atomic charges and dipole moments of atoms characterizing their polarization, and the atomic bond populations. We predict a considerable increase of the TiuO chemical bond covalency near the ~110! surface, as compared to both the bulk and the ~100! surface. The O-terminated ~110! surface has surface energy close to that for ~100!, which indicates that both ~110! and ~100! SrTiO3 surfaces can coexist in polycrystals and perovskite…