2,915 research outputs found
Intrinsic and Rashba Spin-orbit Interactions in Graphene Sheets
Starting from a microscopic tight-binding model and using second order
perturbation theory, we derive explicit expressions for the intrinsic and
Rashba spin-orbit interaction induced gaps in the Dirac-like low-energy band
structure of an isolated graphene sheet. The Rashba interaction parameter is
first order in the atomic carbon spin-orbit coupling strength and first
order in the external electric field perpendicular to the graphene plane,
whereas the intrinsic spin-orbit interaction which survives at E=0 is second
order in . The spin-orbit terms in the low-energy effective Hamiltonian
have the form proposed recently by Kane and Mele. \textit{Ab initio} electronic
structure calculations were performed as a partial check on the validity of the
tight-binding model.Comment: 5 pages, 2 figures; typos corrected, references update
The boundary integral method for magnetic billiards
We introduce a boundary integral method for two-dimensional quantum billiards
subjected to a constant magnetic field. It allows to calculate spectra and wave
functions, in particular at strong fields and semiclassical values of the
magnetic length. The method is presented for interior and exterior problems
with general boundary conditions. We explain why the magnetic analogues of the
field-free single and double layer equations exhibit an infinity of spurious
solutions and how these can be eliminated at the expense of dealing with
(hyper-)singular operators. The high efficiency of the method is demonstrated
by numerical calculations in the extreme semiclassical regime.Comment: 28 pages, 12 figure
A mixed ultrasoft/normconserved pseudopotential scheme
A variant of the Vanderbilt ultrasoft pseudopotential scheme, where the
normconservation is released for only one or a few angular channels, is
presented. Within this scheme some difficulties of the truly ultrasoft
pseudopotentials are overcome without sacrificing the pseudopotential softness.
i) Ghost states are easily avoided without including semicore shells. ii) The
ultrasoft pseudo-charge-augmentation functions can be made more soft. iii) The
number of nonlocal operators is reduced. The scheme will be most useful for
transition metals, and the feasibility and accuracy of the scheme is
demonstrated for the 4d transition metal rhodium.Comment: 4 pages, 2 figure
The influence of surface stress on the equilibrium shape of strained quantum dots
The equilibrium shapes of InAs quantum dots (i.e., dislocation-free, strained
islands with sizes >= 10,000 atoms) grown on a GaAs (001) substrate are studied
using a hybrid approach which combines density functional theory (DFT)
calculations of microscopic parameters, surface energies, and surface stresses
with elasticity theory for the long-range strain fields and strain relaxations.
In particular we report DFT calculations of the surface stresses and analyze
the influence of the strain on the surface energies of the various facets of
the quantum dot. The surface stresses have been neglected in previous studies.
Furthermore, the influence of edge energies on the island shapes is briefly
discussed. From the knowledge of the equilibrium shape of these islands, we
address the question whether experimentally observed quantum dots correspond to
thermal equilibrium structures or if they are a result of the growth kinetics.Comment: 7 pages, 8 figures, submitted to Phys. Rev. B (February 2, 1998).
Other related publications can be found at
http://www.rz-berlin.mpg.de/th/paper.htm
A real-space, rela-time method for the dielectric function
We present an algorithm to calculate the linear response of periodic systems
in the time-dependent density functional thoery, using a real-space
representation of the electron wave functions and calculating the dynamics in
real time. The real-space formulation increases the efficiency for calculating
the interaction, and the real-time treatment decreases storage requirements and
the allows the entire frequency-dependent response to be calculated at once. We
give as examples the dielectric functions of a simple metal, lithium, and an
elemental insulator, diamond.Comment: 17 pages, Latex, 5 figure
Diffusion of Pt dimers on Pt(111)
We report the results of a density-functional study of the diffusion of Pt
dimers on the (111) surface of Pt. The calculated activation energy of 0.37 eV
is in {\em exact} agreement with the recent experiment of Kyuno {\em et al.}
\protect{[}Surf. Sci. {\bf 397}, 191 (1998)\protect{]}. Our calculations
establish that the dimers are mobile at temperatures of interest for adatom
diffusion, and thus contribute to mass transport. They also indicate that the
diffusion path for dimers consists of a sequence of one-atom and (concerted)
two-atom jumps.Comment: Pour pages postscript formatted, including one figure; submitted to
Physical Review B; other papers of interest can be found at url
http://www.centrcn.umontreal.ca/~lewi
Timesaving Double-Grid Method for Real-Space Electronic-Structure Calculations
We present a simple and efficient technique in ab initio electronic-structure
calculation utilizing real-space double-grid with a high density of grid points
in the vicinity of nuclei. This technique promises to greatly reduce the
overhead for performing the integrals that involves non-local parts of
pseudopotentials, with keeping a high degree of accuracy. Our procedure gives
rise to no Pulay forces, unlike other real-space methods using adaptive
coordinates. Moreover, we demonstrate the potential power of the method by
calculating several properties of atoms and molecules.Comment: 4 pages, 5 figure
- …