48,950 research outputs found
Random-phase-approximation-based correlation energy functionals: Benchmark results for atoms
The random phase approximation (RPA) for the correlation energy functional of
density functional theory has recently attracted renewed interest. Formulated
in terms of the Kohn-Sham (KS) orbitals and eigenvalues, it promises to resolve
some of the fundamental limitations of the local density and generalized
gradient approximations, as for instance their inability to account for
dispersion forces. First results for atoms, however, indicate that the RPA
overestimates correlation effects as much as the orbital-dependent functional
obtained by a second order perturbation expansion on the basis of the KS
Hamiltonian. In this contribution, three simple extensions of the RPA are
examined, (a) its augmentation by an LDA for short-range correlation, (b) its
combination with the second order exchange term, and (c) its combination with a
partial resummation of the perturbation series including the second order
exchange. It is found that the ground state and correlation energies as well as
the ionization potentials resulting from the extensions (a) and (c) for closed
sub-shell atoms are clearly superior to those obtained with the unmodified RPA.
Quite some effort is made to ensure highly converged RPA data, so that the
results may serve as benchmark data. The numerical techniques developed in this
context, in particular for the inherent frequency integration, should also be
useful for applications of RPA-type functionals to more complex systems.Comment: 11 pages, 7 figure
Dispersion Laws for In-medium Fermions and Gluons in the CFL Phase of QCD
We evaluate several quantities appearing in the effective lagrangian for the
color-flavor locked phase of high density QCD using a formalism which exploits
the approximate decoupling of fermions with energy negative with respect to the
Fermi energy. The effective theory is essentially two-dimensional and exhibits
a Fermi velocity superselection rule, similar to the one found in the Heavy
Quark Effective Theory. Within the formalism we reproduce, using gradient
expansion, the results for the effective parameters of the Nambu-Goldstone
bosons. We also determine the dispersion laws for the gluons. By coupling the
theory to fermions and integrating over the two-dimensional degrees of freedom
we obtain the effective description of in-medium fermions.Comment: 17 pages, LaTex, 2 figures. Version published in Phys. Lett. B with
an arithmetic misprint corrected in eq. (62) (and as a consequence in eqs.
(63), (66) and (73)
Massive quark effects in two flavor color superconductors
The high density effective theory formalism (HDET) is employed to describe
high density QCD with two massive flavors (2SC). The gap equation is derived
and explicitly solved for the gap parameter. The parameters associated to the
pseudo Nambu-Goldstone boson of are evaluated in the limit
and fixed. In particular we find for the velocity of the
NG boson the relation
.Comment: Latex file. 14 pages, 2 figures. Some improvement in the
presentation. 2 references added. Final version to be published in Physics
Letter
Critical comments on the paper "Crossing by a single scalar field on a Dvali-Gabadadze-Porrati brane" by H Zhang and Z-H Zhu [Phys.Rev.D75,023510(2007)]
It is demonstrated that the claim in the paper "Crossing by a
single scalar field on a Dvali-Gabadadze-Porrati brane" by H Zhang and Z-H Zhu
[Phys.Rev.D75,023510(2007)], about a prove that there do not exist scaling
solutions in a universe with dust in a Dvali-Gabadadze-Porrati (DGP) braneworld
scenario, is incorrect.Comment: 5 pages, 8 eps figure
Mission Analysis Program for Solar Electric Propulsion (MAPSEP). Volume 2: User's manual
A user's manual which describes input/output routines and recommended operating procedures relating to MAPSEP is presented. Samples runs are included
Mission Analysis Program for Solar Electric Propulsion (MAPSEP). Volume 1: Analytical manual
The mission analysis program for solar electric propulsion (MAPSEP) is comprised of the basic modes: TOPSEP (trajectory generation), GODSEP (linear error analysis), and SIMSEP (simulation). The program is designed to analyze any low thrust mission with respect to trajectory performance, guidance and navigation, and to provide system related requirements for the purpose of vehicle design. The MAPSEP organization is described along with all models and algorithms. Topics discussed include: trajectory and error covariance propagation methods, orbit determination processes, thrust modeling, and trajectory correction (guidance) schemes
Mission Analysis Program for Solar Electric Propulsion (MAPSEP). Volume 3: Program manual
The internal structure of MAPSEP is described. Topics discussed include: macrologic, variable definition, subroutines, and logical flow. Information is given to facilitate modifications to the models and algorithms of MAPSEP
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