Search results for "Quantum"
showing 10 items of 9714 documents
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…
Vassiliev invariants for braids on surfaces
2000
We show that Vassiliev invariants separate braids on a closed oriented surface, and we exhibit an universal Vassiliev invariant for these braids in terms of chord diagrams labeled by elements of the fundamental group of the considered surface.
Deducing a Drain Spacing Formula by Applying Dimensional Analysis and Self-Similarity Theory
2016
For designing a steady state drainage system a drain flow formula coupled with the Dupuit-Forcheimer form of the differential equation of groundwater flow is used. At first, in this paper the most applied drain flow formulas in steady-state conditions are reviewed and compared using as dependent variable the ratio between the maximum water table height and the distance between two lines of parallel drains. These equation are also tested using experimental field data measured in three plot drained by surface pipe drains having different value of drain spacing. Then, applying the dimensional analysis and the self-similarity theory, a new drain spacing formula is theoretically deduced and comp…
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…
AB INITIO CALCULATIONS OF SrTiO3, BaTiO3, PbTiO3, CaTiO3 AND BaZrO3 (001) AND (011) SURFACES
2009
I present results of calculations of surface relaxations and rumplings for the (001) and (011) surfaces of BaZrO3 and ATiO3 perovskites (A = Sr, Ba, Pb and Ca) using a hybrid B3PW description of exchange and correlation. The (001) surface energies of AO, TiO2 and ZrO2 terminations are found to be comparable with each other for all five materials. The surface energies for BaZrO3, SrTiO3, BaTiO3, PbTiO3 and CaTiO3 (011) surfaces for all terminations are considerably larger than for (001) surfaces. We predict a considerable increase in the Ti-O (Zr-O) chemical bond covalency near the (011) surface as compared both to the bulk and to the (001) surface.
Rashba splitting of the Tamm surface state on Re(0001) observed by spin-resolved photoemission and scanning tunneling spectroscopy
2020
Physical review research 2(1), 013296 (2020). doi:10.1103/PhysRevResearch.2.013296
Theoretical Simulations of Surface Relaxation for Perovskite Titanates
2000
The (100) and (110) surface relaxations are calculated for SrTiO3 and BaTiO3 perovskite thin films Using a semiempirical shell model, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are calculated. Surface rumpling and surface-induced dipole moments perpendicular to the surface are calculated for different surface terminations. Surface relaxation is found much larger for the (110) surface. Our results for the (100) surfaces are compared with ab initio calculations and LEED experiments.