9,732 research outputs found
Comment on ``A quantum-classical bracket that satisfies the Jacobi identity'' [J. Chem. Phys. 124, 201104 (2006)]
It shown that the quantum-classical dynamical bracket recently proposed in J.
Chem. Phys. 124, 201104 (2006) fails to satisfy the Jacobi identity.Comment: 2 pages, no figure
Nonlinear phase shift from photon-photon scattering in vacuum
We show that QED nonlinear effects imply a phase correction to the linear
evolution of electromagnetic waves in vacuum. We provide explicit solutions of
the modified Maxwell's equations for the propagation of a superposition of two
plane waves, and calculate analytically and numerically the corresponding phase
shift. This provides a new framework for the search of all-optical signatures
of photon-photon scattering in vacuum. In particular, we propose an experiment
for measuring the phase shift in projected high-power laser facilities.Comment: 4 pages, 1 figure. Some references were added, and the comparison
with AC Kerr effect has been improve
Comment on 'Quantum Backreaction on "Classical" Variables'
It is argued that the bracket of Anderson's canonical theory should have been
antisymmetric otherwise serious controversies arise like violation of both
hermiticity and the Leibniz rule of differentiation.Comment: 3 pages, LaTe
Performance of the modified Becke-Johnson potential
Very recently, in the 2011 version of the Wien2K code, the long standing
shortcome of the codes based on Density Functional Theory, namely, its
impossibility to account for the experimental band gap value of semiconductors,
was overcome. The novelty is the introduction of a new exchange and correlation
potential, the modified Becke-Johnson potential (mBJLDA). In this paper, we
report our detailed analysis of this recent work. We calculated using this
code, the band structure of forty one semiconductors and found an important
improvement in the overall agreement with experiment as Tran and Blaha [{\em
Phys. Rev. Lett.} 102, 226401 (2009)] did before for a more reduced set of
semiconductors. We find, nevertheless, within this enhanced set, that the
deviation from the experimental gap value can reach even much more than 20%, in
some cases. Furthermore, since there is no exchange and correlation energy term
from which the mBJLDA potential can be deduced, a direct optimization procedure
to get the lattice parameter in a consistent way is not possible as in the
usual theory. These authors suggest that a LDA or a GGA optimization procedure
is used previous to a band structure calculation and the resulting lattice
parameter introduced into the 2011 code. This choice is important since small
percentage differences in the lattice parameter can give rise to quite higher
percentage deviations from experiment in the predicted band gap value.Comment: 10 pages, 2 figures, 5 Table
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