1,772 research outputs found
The quasiparticle band gap in the topological insulator Bi2Te3
We present a theoretical study of dispersion of states which form the bulk
band-gap edges in the three-dimensional topological insulator Bi2Te3. Within
density functional theory, we analyze the effect of atomic positions varying
within the error range of the available experimental data and approximation
chosen for the exchange-correlation functional on the bulk band gap and k-space
location of valence- and conduction-band extrema. For each set of the positions
with different exchange-correlation functionals, we show how many-body
corrections calculated within a one-shot GW approach affect the mentioned
characteristics of electronic structure of Bi2Te3. We thus also illustrate to
what degree the one-shot GW results are sensitive to the reference one-particle
band structure in the case of bismuth telluride. We found that for this
topological insulator the GW corrections enlarge the fundamental band gap and
for certain atomic positions and reference band structure bring its value in
close agreement with experiment.Comment: 12 pages, 6 figures, 5 table
Towards an ab Initio, description of adsorbate vibrations
This thesis investigates accurate theoretical prediction of anharmonic vibrational frequencies of molecules adsorbed on metal surfaces. Such adsorbed systems are composed of two parts with dierent electronic properties, the adsorbate and the surface. However, most existing quantum mechanical methods are not identically accurate for both parts. Moreover, methods that can accurately describe extended system are very time consuming and signicantly complicates their usage for standard anharmonic calculations.This thesis introduces a fragment method to overcome this difficulty. Within our method an energy correction is computed using high-level ab initio quantum mechanical method by considering an adsorbed molecule separately from the metal surface. The reliability of this approach is demonstrated for two test systems: an acetylene molecule adsorbed on a Cu(001) surface and a thiophene molecule adsorbed on a Au(111) surface. In both cases intra-adsorbate anharmonic frequencies obtained using the fragment method show better agreement with experimental data than the corresponding anharmonic frequencies computed using a standard approach. Moreover, a correlation between the accuracy of the fragment method and the accuracy of the ab initio method used for adsorbed molecule is observed. This correlation provides a way to systematically improve adsorbate frequencies by improving the quality of the potential energy surface used.Finally, for each test systems we established a correlation between the strength of adsorption and the value of the frequencies shift upon adsorption. This allows us to conclude that terthiophene is only weakly adsorbed on a Au(111) surface based on the similarity between the adsorbate and the gas-phase vibrational spectra
Nonlocal Edge State Transport in Topological Insulators
We use the N-terminal scheme for studying the edge state transportin in
two-dimensional topological insulators. We find the universal nonlocal response
in the ballistic transport approach. This macroscopic exhibition of the
topological order offers different areas for applications.Comment: Updated to published versio
Competing rhombohedral and monoclinic crystal structures in Mn compounds: an {\em ab-initio} study
Based on the relativistic spin-polarized density functional theory
calculations we investigate the crystal structure, electronic and magnetic
properties of a family MnPn2Ch4 compounds, where pnictogen metal atoms (Pn) are
Sb and Bi; chalcogens (Ch) are Se, Te. We show that in the series the compounds
of this family with heavier elements prefer to adopt rhombohedral crystal
structure composed of weakly bonded septuple monoatomic layers while those with
lighter elements tend to be in the monoclinic structure. Irrespective of the
crystal structure all compounds of the MnPn2Ch4 series demonstrate a weak
energy gain (of a few meV per formula unit or even smaller than meV) for
antiferromagnetic (AFM) coupling for magnetic moments on Mn atoms with respect
to their ferromagnetic (FM) state. For rhombohedral structures the interlayer
AFM coupling is preferable while in monoclinic phases intralayer AFM
configuration with ferromagnetic ordering along the Mn chain and
antiferromagnetic ordering between the chains has a minimum energy. Over the
series the monoclinic compounds are characterized by substantially wider
bandgap than compounds with rhombohedral structure
Electron-phonon interaction at the Be(0001) surface
We present a first principle study of the electron-phonon (e-p) interaction
at the Be(0001) surface. The real and imaginary part of the e-p self energy are
calculated for the surface state in the binding energy range from the
point to the Fermi level. Our calculation shows an overall good
agreement with several photoemission data measured at high and low
temperatures. Additionally, we show that the energy derivative of real part of
the self-energy presents a strong temperature and energy variation close to
, making it difficult to measure its value just at .Comment: Accepted in Phys. Rev. Lett., 5 figure
Topological phase states of the SU(3) QCD
We consider the topologically nontrivial phase states and the corresponding
topological defects in the SU(3) d-dimensional quantum chromodynamics (QCD).
The homotopy groups for topological classes of such defects are calculated
explicitly. We have shown that the three nontrivial groups are pi_3 SU(3)=Z,
pi_5 SU(3)=Z, and pi_6 SU(3)=Z_6 if 3 < d < 6. The latter result means that we
are dealing exactly with six topologically different phase states. The
topological invariants for d=3,5,6 are described in detail.Comment: LATEX2e, 5 page
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