An adaptive algorithm for n-body field expansions
Weinberg, Martin D.
1998-05-28
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Popular density functionals for the exchange-correlation energy typically
fail to reproduce the degeneracy of different ground states of open-shell
atoms. As a remedy, functionals which explicitly depend on the current density
have been suggested. We present an analysis of this problem by investigating
functionals that explicitly depend on the Kohn-Sham orbitals. Going beyond the
exact-exchange approximation by adding correlation in the form of the
Colle-Salvetti functional we show how current-dependent terms enter the
Colle-Salvetti expression and their relevance is evaluated. A very good
description of the degeneracy of ground-states for atoms of the first and
second row of the periodic table is obtained.
Comment: Hydrogen atom and negative ion model for simple donor type
semiconductors
Comment: 6 pages, 6 figures. Submitted to J. Nanosci. Nanotech
By means of low-temperature expansions (LTEs), the nucleation free energy and
the precipitate interface free energy are expressed as functions of the
solubility limit for alloys which lead to the precipitation of a stoichiometric
L12 compound such as Al-Sc or Al-Zr alloys. Classical nucleation theory is then
used to obtain a simple expression of the nucleation rate whose validity is
demonstrated by a comparison with atomic simulations. LTEs also explain why
simple mean-field approximation like the Bragg-Williams approximation fails to
predict correct nucleation rates in such an ordering alloy.
The nucleation of carbon nanotubes on small nickel clusters is studied using
a tight binding model coupled to grand canonical Monte Carlo simulations. This
technique closely follows the conditions of the synthesis of carbon nanotubes
by chemical vapor deposition. The possible formation of a carbon cap on the
catalyst particle is studied as a function of the carbon chemical potential,
for particles of different size, either crystalline or disordered. We show that
these parameters strongly influence the structure of the cap/particle interface
which in turn will have a strong effect on the control of the structure of the
nanotube. In particular, we discuss the presence of carbon on surface or in
subsurface layers.
Comment: Proceedings of the 13th Brazilian Workshop on Semiconductors Physics
Comment: Will appear as a Comment in CPL, on the paper cited above that is
also available at arXiv:cond-mat/0611428
Melting of a bicrystal along the grain boundary is discussed. A triple
junction plays a crucial role in the velocity selection problem in this case.
In some range of the parameters an entirely analytical solution of this problem
is given. This allows to present a transparent picture of the structure of the
selection theory. We also discuss the selection problem in the case of the
growth of a ``eutectoid dendrite'' where a triple junction is present because
three phases are involved in the eutectoid reaction.
