An adaptive algorithm for n-body field expansions
Weinberg, Martin D.
1998-05-28
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The electronic band structures and optical properties of cubic, tetragonal,
and monoclinic phases of HfO2 are calculated using the first-principles linear
augmented plane-wave method, within the density functional theory and
generalized gradient approximation, and taking into account full-relativistic
contributions. From the band structures, the electron- and hole-effective
masses were obtained. Relativistic effects play an important role, which is
reflected in the effective masses values and in the detailed structure of the
dielectric function. The calculated imaginary part of the dielectric function
and refractive index are in good agreement with the data reported in the
literature.
Epitaxial self-assembled quantum dots (SAQDs) are of interest for
nanostructured optoelectronic and electronic devices such as lasers,
photodetectors and nanoscale logic. Spatial order and size order of SAQDs are
important to the development of usable devices. It is likely that these two
types of order are strongly linked; thus, a study of spatial order will also
have strong implications for size order. Here a study of spatial order is
undertaken using a linear analysis of a commonly used model of SAQD formation
based on surface diffusion. Analytic formulas for film-height correlation
functions are found that characterize quantum dot spatial order and
corresponding correlation lengths that quantify order. Initial atomic-scale
random fluctuations result in relatively small correlation lengths (about two
dots) when the effect of a wett...
Comment: 3 pages, 3 figures. JACS, 2007, in press
Comment: 19 pages, 4 figures, to appear in PRB
Comment: 20 pages, 13 figures, to be published in PRB
Classical effective potentials are indispensable for any large-scale
atomistic simulations, and the relevance of simulation results crucially
depends on the quality of the potentials used. For complex alloys like
quasicrystals, however, realistic effective potentials are practically
inexistent. We report here on our efforts to develop effective potentials
especially for quasicrystalline alloy systems. We use the so-called force
matching method, in which the potential parameters are adapted so as to
optimally reproduce the forces and energies in a set of suitably chosen
reference configurations. These reference data are calculated with ab-initio
methods. As a first application, EAM potentials for decagonal Al-Ni-Co,
icosahedral Ca-Cd, and both icosahedral and decagonal Mg-Zn quasicrystals have
been constructed. The influence of the po...
Comment: Submitted to Phys. Rev. Letters
We investigate the bonding of H in O vacancies of ZnO using density
functional calculations. We find that H is anionic and does not form
multicenter bonds with Zn in this compound.
We present an x-ray spectromicroscopic investigation of single-crystalline
magnetic FeMn/Co bilayers on Cu(001), using X-ray magnetic circular (XMCD) and
linear (XMLD) dichroism at the Co and Fe L3 absorption edges in combination
with photoelectron emission microscopy (PEEM). Using the magnetic coupling
between the ferromagnetic Co layer and the antiferromagnetic FeMn layer we are
able to produce magnetic domains with two different crystallographic
orientations of the magnetic easy axis within the same sample at the same time.
We find a huge difference in the XMLD contrast between the two types of
magnetic domains, which we discuss in terms of intrinsic magneto-crystalline
anisotropy of XMLD of the Co layer. We also demonstrate that due to the high
sensitivity of the method, the small number of induced ferromagnetic Fe moments
at the...
