40,676 research outputs found
Role of exchange interaction in self-consistent calculations of endohedral fullerenes
Results of the self-consistent calculation of electronic structure of
endohedral fullerene Ar@C within the Hartree-Fock and the local density
approximations are presented. Hartree-Fock approximation is used for the
self-consistent description for the first time. It is shown that the accurate
account of the exchange interaction between all electrons of the compound leads
to the significant modification of the atomic valent shell which causes the
noticeable charge redistribution inside the endohedral compound.Comment: 5 figures, Proceedings of the 5th Conference on Elementary Processes
in Atomic Systems (CEPAS 2011), submitted to Nuclear Instruments and Methods
in Physics Research Section
Spatial and spin symmetry breaking in semidefinite-programming-based Hartree-Fock theory
The Hartree-Fock problem was recently recast as a semidefinite optimization
over the space of rank-constrained two-body reduced-density matrices (RDMs)
[Phys. Rev. A 89, 010502(R) (2014)]. This formulation of the problem transfers
the non-convexity of the Hartree-Fock energy functional to the rank constraint
on the two-body RDM. We consider an equivalent optimization over the space of
positive semidefinite one-electron RDMs (1-RDMs) that retains the non-convexity
of the Hartree-Fock energy expression. The optimized 1-RDM satisfies ensemble
-representability conditions, and ensemble spin-state conditions may be
imposed as well. The spin-state conditions place additional linear and
nonlinear constraints on the 1-RDM. We apply this RDM-based approach to several
molecular systems and explore its spatial (point group) and spin ( and
) symmetry breaking properties. When imposing and symmetry but
relaxing point group symmetry, the procedure often locates
spatial-symmetry-broken solutions that are difficult to identify using standard
algorithms. For example, the RDM-based approach yields a smooth,
spatial-symmetry-broken potential energy curve for the well-known Be--H
insertion pathway. We also demonstrate numerically that, upon relaxation of
and symmetry constraints, the RDM-based approach is equivalent to
real-valued generalized Hartree-Fock theory.Comment: 9 pages, 6 figure
A New Method and a New Scaling For Deriving Fermionic Mean-field Dynamics
We introduce a new method for deriving the time-dependent Hartree or
Hartree-Fock equations as an effective mean-field dynamics from the microscopic
Schroedinger equation for fermionic many-particle systems in quantum mechanics.
The method is an adaption of the method used in [Pickl, Lett. Math. Phys.,
97(2):151-164, 2011] for bosonic systems to fermionic systems. It is based on a
Gronwall type estimate for a suitable measure of distance between the
microscopic solution and an antisymmetrized product state. We use this method
to treat a new mean-field limit for fermions with long-range interactions in a
large volume. Some of our results hold for singular attractive or repulsive
interactions. We can also treat Coulomb interaction assuming either a mild
singularity cutoff or certain regularity conditions on the solutions to the
Hartree(-Fock) equations. In the considered limit, the kinetic and interaction
energy are of the same order, while the average force is subleading. For some
interactions, we prove that the Hartree(-Fock) dynamics is a more accurate
approximation than a simpler dynamics that one would expect from the subleading
force. With our method we also treat the mean-field limit coupled to a
semiclassical limit, which was discussed in the literature before, and we
recover some of the previous results. All results hold for initial data close
(but not necessarily equal) to antisymmetrized product states and we always
provide explicit rates of convergence.Comment: 42 pages, LaTex; v2: introduction expanded, presentation of main
results improved, several minor improvements and references adde
Spontaneous coherence and the quantum Hall Effect in triple-layer electron systems
We investigate spontaneous interlayer phase coherence and the occurrence of
the quantum Hall effect in triple-layer electron systems. Our work is based on
a simple tight-binding model that greatly facilitates calculations and whose
accuracy is verified by comparison with recent experiments. By calculating the
ground state in an unrestricted Hartree-Fock approximation and the
collective-mode spectrum in a time-dependent Hartree-Fock approximation, we
construct a phase diagram delimiting regions in the parameter space of the
model where the integer quantum Hall effect occurs in the absence of interlayer
tunneling.Comment: To appear in Phys. Rev. B, 20 pages, 5 PostScript figures uuencoded
with TeX fil
Spontaneous Coherence and Collective Modes in Double-Layer Quantum Dot Systems
We study the ground state and the collective excitations of
parabolically-confined double-layer quantum dot systems in a strong magnetic
field. We identify parameter regimes where electrons form maximum density
droplet states, quantum-dot analogs of the incompressible states of the bulk
integer quantum Hall effect. In these regimes the Hartree-Fock approximation
and the time-dependent Hartree-Fock approximations can be used to describe the
ground state and collective excitations respectively. We comment on the
relationship between edge excitations of dots and edge magneto-plasmon
excitations of bulk double-layer systems.Comment: 20 pages (figures included) and also available at
http://fangio.magnet.fsu.edu/~jhu/Paper/qdot_cond.ps, replaced to fix figure
Effect of Pauli repulsion and transfer on fusion
The effect of the Pauli exclusion principle on the nucleus-nucleus bare
potential is studied using a new density-constrained extension of the
Frozen-Hartree-Fock (DCFHF) technique. The resulting potentials exhibit a
repulsion at short distance. The charge product dependence of this Pauli
repulsion is investigated. Dynamical effects are then included in the potential
with the density-constrained time-dependent Hartree-Fock (DCTDHF) method. In
particular, isovector contributions to this potential are used to investigate
the role of transfer on fusion, resulting in a lowering of the inner part of
the potential for systems with positive Q-value transfer channels.Comment: Proceedings of an invited talk given at FUSION17, Hobart, Tasmania,
AU (20-24 February, 2017
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