184 research outputs found
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
Kirzhnits gradient expansion for a D-dimensional Fermi gas
For an ideal D-dimensional Fermi gas under generic external confinement we
derive the correcting coefficient of the von Weizsacker term in the
kinetic energy density. To obtain this coefficient we use the Kirzhnits
semiclassical expansion of the number operator up to the second order in the
Planck constant . Within this simple and direct approach we determine
the differential equation of the density profile and the density functional of
the Fermi gas. In the case D=2 we find that the Kirzhnits gradient corrections
vanish to all order in .Comment: 6 pages, 0 figures, accepted for publication in J. Phys. A: Math.
Theo
Simple model of the static exchange-correlation kernel of a uniform electron gas with long-range electron-electron interaction
A simple approximate expression in real and reciprocal spaces is given for
the static exchange-correlation kernel of a uniform electron gas interacting
with the long-range part only of the Coulomb interaction. This expression
interpolates between the exact asymptotic behaviors of this kernel at small and
large wave vectors which in turn requires, among other thing, information from
the momentum distribution of the uniform electron gas with the same interaction
that have been calculated in the G0W0 approximation. This exchange-correlation
kernel as well as its complement analogue associated to the short-range part of
the Coulomb interaction are more local than the Coulombic exchange-correlation
kernel and constitute potential ingredients in approximations for recent
adiabatic connection fluctuation-dissipation and/or density functional theory
approaches of the electronic correlation problem based on a separate treatment
of long-range and short-range interaction effects.Comment: 14 pages, 14 figures, to be published in Phys. Rev.
Polarizational stopping power of heavy-ion diclusters in two-dimensional electron liquids
The in-plane polarizational stopping power of heavy-ion diclusters in a
two-dimensional strongly coupled electron liquid is studied. Analytical
expressions for the stopping power of both fast and slow projectiles are
derived. To go beyond the random-phase approximation we make use of the inverse
dielectric function obtained by means of the method of moments and some recent
analytical expressions for the static local-field correction factor.Comment: 9 pages, 5 figures. Published in Physical Review B
http://link.aps.org/abstract/PRB/v75/e11510
Damping of long-wavelength collective excitations in quasi-onedimensional Fermi liquids
The imaginary part of the exchange-correlation kernel in the longitudinal
current-current response function of a quasi-onedimensional Fermi liquid is
evaluated by an approximate decoupling in the equation of motion for the
current density, which accounts for processes of excitation of two
particle-hole pairs. The two-pair spectrum determines the intrinsic damping
rate of long-wavelength collective density fluctuations, which is calculated
and contrasted with a result previously obtained for a clean Luttinger liquid.Comment: 9 pages, no figures, Physica B in pres
Scaling in the correlation energies of two-dimensional artificial atoms
We find an unexpected scaling in the correlation energy of artificial atoms,
i.e., harmonically confined two-dimensional quantum dots. The scaling relation
is found through extensive numerical examinations including Hartree-Fock,
variational quantum Monte Carlo, density-functional, and full
configuration-interaction calculations. We show that the correlation energy,
i.e., the true ground-state total energy subtracted by the Hartree-Fock total
energy, follows a simple function of the Coulomb energy, confimenent strength
and, the number of electrons. We find an analytic expression for this function,
as well as for the correlation energy per particle and for the ratio between
the correlation and total energies. Our tests for independent diffusion Monte
Carlo and coupled-cluster results for quantum dots -- including open-shell data
-- confirm the generality of the obtained scaling. As the scaling is also well
applicable to 100 electrons, our results give interesting prospects
for the development of correlation functionals within density-functional
theory.Comment: Accepted to Journal of Physics: Condensed Matte
Analytical expressions for the charge-charge local-field factor and the exchange-correlation kernel of a two-dimensional electron gas
We present an analytical expression for the static many-body local field
factor of a homogeneous two-dimensional electron gas, which
reproduces Diffusion Monte Carlo data and embodies the exact asymptotic
behaviors at both small and large wave number . This allows us to also
provide a closed-form expression for the exchange and correlation kernel
, which represents a key input for density functional studies of
inhomogeneous systems.Comment: 5 pages, 3 figure
Dynamic Many-Body Theory. II. Dynamics of Strongly Correlated Fermi Fluids
We develop a systematic theory of multi-particle excitations in strongly
interacting Fermi systems. Our work is the generalization of the time-honored
work by Jackson, Feenberg, and Campbell for bosons, that provides, in its most
advanced implementation, quantitative predictions for the dynamic structure
function in the whole experimentally accessible energy/momentum regime. Our
view is that the same physical effects -- namely fluctuations of the wave
function at an atomic length scale -- are responsible for the correct
energetics of the excitations in both Bose and Fermi fluids. Besides a
comprehensive derivation of the fermion version of the theory and discussion of
the approximations made, we present results for homogeneous He-3 and electrons
in three dimensions. We find indeed a significant lowering of the zero sound
mode in He-3 and a broadening of the collective mode due to the coupling to
particle-hole excitations in good agreement with experiments. The most visible
effect in electronic systems is the appearance of a ``double-plasmon''
excitation.Comment: submitted to Phys. Rev.
Exact exchange potential evaluated solely from occupied Kohn-Sham and Hartree-Fock solutions
The reported new algorithm determines the exact exchange potential v_x in a
iterative way using energy and orbital shifts (ES, OS) obtained - with
finite-difference formulas - from the solutions (occupied orbitals and their
energies) of the Hartree-Fock-like equation and the Kohn-Sham-like equation,
the former used for the initial approximation to v_x and the latter - for
increments of ES and OS due to subsequent changes of v_x. Thus, solution of the
differential equations for OS, used by Kummel and Perdew (KP) [Phys. Rev. Lett.
90, 043004 (2003)], is avoided. The iterated exchange potential, expressed in
terms of ES and OS, is improved by modifying ES at odd iteration steps and OS
at even steps. The modification formulas are related to the OEP equation
(satisfied at convergence) written as the condition of vanishing density shift
(DS) - they are obtained, respectively, by enforcing its satisfaction through
corrections to approximate OS and by determining optimal ES that minimize the
DS norm. The proposed method, successfully tested for several closed-(sub)shell
atoms, from Be to Kr, within the DFT exchange-only approximation, proves highly
efficient. The calculations using pseudospectral method for representing
orbitals give iterative sequences of approximate exchange potentials (starting
with the Krieger-Li-Iafrate approximation) that rapidly approach the exact v_x
so that, for Ne, Ar and Zn, the corresponding DS norm becomes less than 10^{-6}
after 13, 13 and 9 iteration steps for a given electron density. In
self-consistent density calculations, orbital energies of 10^{-4} Hartree
accuracy are obtained for these atoms after, respectively, 9, 12 and 12 density
iteration steps, each involving just 2 steps of v_x iteration, while the
accuracy limit of 10^{-6}--10^{-7} Hartree is reached after 20 density
iterations.Comment: 21 pages, 5 figures, 3 table
Exchange and correlation energies of ground states of atoms and molecules in strong magnetic fields
Using a Hartree-Fock mesh method and a configuration interaction approach
based on a generalized Gaussian basis set we investigate the behaviour of the
exchange and correlation energies of small atoms and molecules, namely th e
helium and lithium atom as well as the hydrogen molecule, in the presence of a
magnetic field covering the regime B=0-100a.u. In general the importance of the
exchange energy to the binding properties of at oms or molecules increases
strongly with increasing field strength. This is due to the spin-flip
transitions and in particular due to the contributions of the tightly bound
hydrogenic state s which are involved in the corresponding ground states of
different symmetries. In contrast to the exchange energy the correlation energy
becomes less relevant with increasing field strength. This holds for the
individual configurations constituting the ground state and for the crossovers
of the global ground state.Comment: 4 Figures acc.f.publ.in Phys.Rev.
- …