120 research outputs found
A Hybrid Decomposition Parallel Implementation of the Car-Parrinello Method
We have developed a flexible hybrid decomposition parallel implementation of
the first-principles molecular dynamics algorithm of Car and Parrinello. The
code allows the problem to be decomposed either spatially, over the electronic
orbitals, or any combination of the two. Performance statistics for 32, 64, 128
and 512 Si atom runs on the Touchstone Delta and Intel Paragon parallel
supercomputers and comparison with the performance of an optimized code running
the smaller systems on the Cray Y-MP and C90 are presented.Comment: Accepted by Computer Physics Communications, latex, 34 pages without
figures, 15 figures available in PostScript form via WWW at
http://www-theory.chem.washington.edu/~wiggs/hyb_figures.htm
Proximity-induced spin-orbit coupling in phosphorene on WSe monolayer
We investigate, using first-principles methods and effective-model
simulations, the spin-orbit coupling proximity effects in a bilayer
heterostructure comprising phosphorene and WSe monolayers. We specifically
analyze holes in phosphorene around the point, at which we find a
significant increase of the spin-orbit coupling that can be attributed to the
strong hybridization of phosphorene with the WSe bands. We also propose an
effective spin-orbit model based on the symmetry of the
studied heterostructure. The corresponding spin-orbit field can be divided into
two parts: the in-plane field, present due to the broken nonsymmorphic
horizontal glide mirror plane symmetry, and the dominant out-of-plane field
triggered by breaking the out-of-plane rotational symmetry of the phosphorene
monolayer. Furthermore, we also demonstrate that a heterostructure with
60 twist angle exhibits an opposite out-of-plane spin-orbit field,
indicating that the coupling can effectively be tuned by twisting. The studied
phosphorene/WSe bilayer is a prototypical low common-symmetry
heterostructure in which the proximity effect can be used to engineer the spin
texture of the desired material.Comment: 7 pages, 3 figure
The Ab-Initio Simulation of the Liquid Ga-Se System
Ab-initio dynamical simulation is used to study the liquid Ga-Se system at
the three concentrations GaSe, GaSe and GaSe at the temperature
1300~K. The simulations are based on the density functional pseudopotential
technique, with the system maintained on the Born-Oppenheimer surface by
conjugate gradients minimization. We present results for the partial structure
factors and radial distribution functions, which reveal how the liquid
structure depends on the composition. Our calculations of the electrical
conductivity using the Kubo-Greenwood approximation show that
depends very strongly on the composition. We show how this variation of
is related to the calculated electronic density of states. Comparisons
with recent experimental determinations of the structure and conductivity are
also presented.Comment: REVTEX, 8 pages, 4 uuencoded poscript figures,
([email protected]
Comment on ``Local dimer-adatom stacking fault structures from 3x3 to 13x13 along Si(111)-7x7 domain boundaries''
Zhao et al. [Phys.Rev.B 58, 13824 (1998)] depicted several atomic structures
of domain boundaries on a Si(111) surface and criticized the article by the
present author and the co-workers. I will point out that their criticism is
incorrect and their structure models have no consistency.Comment: 2 pages. Physical Review B, to appea
Efficient and reliable method for the simulation of scanning tunneling images and spectra with local basis sets
Based on Bardeen's perturbative approach to tunneling, we have found an
expression for the current between tip and sample, which can be efficiently
coded in order to perform fast ab initio simulations of STM images. Under the
observation that the potential between the electrodes should be nearly flat at
typical tunnel gaps, we have addressed the difficulty in the computation of the
tunneling matrix elements by considering a vacuum region of constant potential
delimited by two surfaces (each of them close to tip and sample respectively),
then propagating tip and sample wave functions by means of the vacuum Green's
function, to finally obtain a closed form in terms of convolutions. The current
is then computed for every tip-sample relative position and for every bias
voltage in one shot. The electronic structure of tip and sample is calculated
at the same footing, within density functional theory, and independently. This
allows us to carry out multiple simulations for a given surface with a database
of different tips. We have applied this method to the Si(111)-(7x7) and
Ge(111)-c(2x8) surfaces. Topographies and spectroscopic data, showing a very
good agreement with experiments, are presented.Comment: 10 pages, 11 figure
The Effect of Compressive and Tensile Strains on the Electron Structure of Phosphorene
A new promising semiconductor material (phosphorene) is studied using theoretical simulation. The possibilities of changing the magnitude and nature of interband transitions under the action of compressive and tensile stresses on the phosphorene crystal lattice are determined. It is found that phosphorene can be both direct-gap and indirect-gap semiconductors, depending on the magnitude and direction of stress action. Phosphorene can be used in new generation nanoelectronic devices with controlled movement of charge carriers
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
Monte Carlo study of Si(111) homoepitaxy
An attempt is made to simulate the homoepitaxial growth of a Si(111) surface
by the kinetic Monte Carlo method in which the standard Solid-on-Solid model
and the planar model of the (7x7) surface reconstruction are used in
combination.
By taking account of surface reconstructions as well as atomic deposition and
migrations, it is shown that the effect of a coorparative stacking
transformation is necessary for a layer growth.Comment: 4 pages, 5 figures. For Fig.1 of this article, please see Fig.2 of
Phys.Rev. B56, 3583 (1997). To appear in Phys.Rev.B. (June 1998
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