3,073 research outputs found
A simple classical mapping of the spin-polarized quantum electron gas: distribution functions and local field corrections
We use the now well known spin-unpolarized exchange-correlation energy E_{xc}
of the uniform electron gas as the basic ``many-body'' input to determine the
temperature T_q of a classical Coulomb fluid having the same correlation energy
as the quantum system. It is shown that the spin-polarized pair distribution
functions (SPDFs) of the classical fluid at T_q, obtained using the
hyper-netted chain (HNC) equation are in excellent agreement with those of the
T=0 quantum fluid obtained by quantum Monte Carlo (QMC) simulations. These
methods are computationally simple and easily applied to problems which are
currently outside the scope of QMC. Results are presented for the SPDFs and the
local-field corrections to the response functions of the electron fluid at zero
and finite temperatures.Comment: 4 pags (Revtex), 3 posscript figure
Spin and Valley dependent analysis of the two-dimensional low-density electron system in Si-MOSFETS
The 2-D electron system (2DES) in Si metal-oxide field-effect transistors
(MOSFETS) consists of two distinct electron fluids interacting with each other.
We calculate the total energy as a function of the density , and the spin
polarization in the strongly-correlated low-density regime, using a
classical mapping to a hypernetted-chain (CHNC) equation inclusive of bridge
terms. Here the ten distribution functions, arising from spin and valley
indices, are self-consistently calculated to obtain the total free energy, the
chemical potential, the compressibility and the spin susceptibility. The T=0
results are compared with the 2-valley Quantum Monte Carlo (QMC) data of Conti
et al. (at T=0, ) and found to be in excellent agreement. However,
unlike in the one-valley 2DES, it is shown that {\it the unpolarized phase is
always the stable phase in the 2-valley system}, right up to Wigner
Crystallization at . This leads to the insensitivity of to the
spin polarization and to the density. The compressibility and the
spin-susceptibility enhancement calculated from the free energy confirm the
validity of a simple approach to the two-valley response based on coupled-mode
formation. The three methods, QMC, CHNC, and Coupled-mode theory agree closely.
Our results contain no {\it ad hoc} fit parameters. They agree with experiments
and do not invoke impurity effects or metal-insulator transition phenomenology.Comment: 10 pages 4 figure
Idealized Slab Plasma approach for the study of Warm Dense Matter
Recently, warm dense matter (WDM) has emerged as an interdisciplinary field
that draws increasing interest in plasma physics, condensed matter physics,
high pressure science, astrophysics, inertial confinement fusion, as well as
materials science under extreme conditions. To allow the study of well-defined
WDM states, we have introduced the concept of idealized-slab plasmas that can
be realized in the laboratory via (i) the isochoric heating of a solid and (ii)
the propagation of a shock wave in a solid. The application of this concept
provides new means for probing the dynamic conductivity, equation of state,
ionization and opacity. These approaches are presented here using results
derived from first-principles (density-functional type) theory, Thomas-Fermi
type theory, and numerical simulations.Comment: 37 pages, 21 figures, available, pdf file only. To appear in: Laser
and Particle beams. To appear more or less in this form in Laser and Particle
beam
Structure of the Local-field factor of the 2-D electron fluid. Possible evidence for correlated scattering of electron pairs
The static local-field factor (LFF) of the 2-D electron fluid is calculated
{\it nonperturbatively} using a mapping to a classical Coulomb fluid
Phys. Rev. Lett., {\bf 87}, 206. The LFF for the paramagnetic
fluid {\it differs markedly} from perturbation theory where a maximum near
2 is expected. Our LFF has a quasi-linear small-k region leading to a
maximum close to 3, in agreent with currently available quantum Monte
Carlo data. The structure in the LFF and its dependence on the density and
temperature are interpretted as a signature of correlated scattering of
electron pairs of opposite spin.The lack of structure at implies
weakened Friedel oscillations, Kohn anomalies etc.Comment: 4 pages, 3 figures, version 2 of condmat/0304034, see
http://nrcphy1.phy.nrc.ca/ims/qp/chandre/chnc/ Changs in the text, figure 2
and updated reference
The Equation of State and the Hugoniot of Laser Shock-Compressed Deuterium
The equation of state and the shock Hugoniot of deuterium are calculated
using a first-principles approach, for the conditions of the recent shock
experiments. We use density functional theory within a classical mapping of the
quantum fluids [ Phys. Rev. Letters, {\bf 84}, 959 (2000) ]. The calculated
Hugoniot is close to the Path-Integral Monte Carlo (PIMC) result. We also
consider the {\it quasi-equilibrium} two-temperature case where the Deuterons
are hotter than the electrons; the resulting quasi-equilibrium Hugoniot mimics
the laser-shock data. The increased compressibility arises from hot
pairs occuring close to the zero of the electron chemical potential.Comment: Four pages; One Revtex manuscript, two postscipt figures; submitted
to PR
Quantum Brayton cycle with coupled systems as working substance
We explore the quantum version of Brayton cycle with a composite system as
the working substance. The actual Brayton cycle consists of two adiabatic and
two isobaric processes. Two pressures can be defined in our isobaric process,
one corresponds to the external magnetic field (characterized by ) exerted
on the system, while the other corresponds to the coupling constant between the
subsystems (characterized by ). As a consequence, we can define two types
of quantum Brayton cycle for the composite system. We find that the subsystem
experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized
by ), whereas the subsystem's cycle is of quantum Otto in another Brayton
cycle (characterized by ). The efficiency for the composite system equals
to that for the subsystem in both cases, but the work done by the total system
are usually larger than the sum of work done by the two subsystems. The other
interesting finding is that for the cycle characterized by , the subsystem
can be a refrigerator while the total system is a heat engine. The result in
the paper can be generalized to a quantum Brayton cycle with a general coupled
system as the working substance.Comment: 7 pages, 3 figures, accepted by Phys. Rev.
Spin-dependent correlation in two-dimensional electron liquids at arbitrary degeneracy and spin-polarization: CHNC approach
We apply the classical mapping technique developed recently by Dharma-wardana
and Perrot for a study of the uniform two-dimensional electron system at
arbitrary degeneracy and spin-polarization. Pair distribution functions,
structure factors, the Helmhotz free energy, and the compressibility are
calculated for a wide range of parameters. It is shown that at low temperatures
T/ T_F <0.1, T_F being the Fermi temperature, our results almost reduce to
those of zero-temperature analyses. In the region T/ T_F >= 1, the finite
temperature effects become considerable at high densities for all
spin-polarizations. We find that, in our approximation without bridge
functions, the finite temperature electron system in two dimensions remains to
be paramagnetic fluid until the Wigner crystallization density. Our results are
compared with those of three-dimensional system and indicated are the
similarities in temperature, spin-polarization, and density dependencies of
many physical properties.Comment: 8 pages, 9 figure
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