464 research outputs found
Variational Monte Carlo for Interacting Electrons in Quantum Dots
We use a variational Monte Carlo algorithm to solve the electronic structure
of two-dimensional semiconductor quantum dots in external magnetic field. We
present accurate many-body wave functions for the system in various magnetic
field regimes. We show the importance of symmetry, and demonstrate how it can
be used to simplify the variational wave functions. We present in detail the
algorithm for efficient wave function optimization. We also present a Monte
Carlo -based diagonalization technique to solve the quantum dot problem in the
strong magnetic field limit where the system is of a multiconfiguration nature.Comment: 34 pages, proceedings of the 1st International Meeting on Advances in
Computational Many-Body Physics, to appear in Journal of Low Temperature
Physics (vol. 140, nos. 3/4
Stability of light positronic atoms: Quantum Monte Carlo studies
We present accurate ground-state energies for the positronium atom in a Coulomb field of point charge Z (XZPs), for the positronium hydrogen (HPs) and positronium lithium (LiPs) atoms. Calculations are done using the diffusion quantum Monte Carlo (DQMC) method. For XZPs, the critical value of Z for binding is examined. While HPs is stable, the results show that LiPs is unstable against dissociation to a lithium atom and a positronium.Peer reviewe
Interacting electrons on a quantum ring: exact and variational approach
We study a system of interacting electrons on a one-dimensional quantum ring
using exact diagonalization and the variational quantum Monte Carlo method. We
examine the accuracy of the Slater-Jastrow -type many-body wave function and
compare energies and pair distribution functions obtained from the two
approaches. Our results show that this wave function captures most correlation
effects. We then study the smooth transition to a regime where the electrons
localize in the rotating frame, which for the ultrathin quantum ring system
happens at quite high electron density.Comment: 19 pages, 10 figures. Accepted for publication in the New Journal of
Physic
Electron correlations, spontaneous magnetization and momentum density in quantum dots
The magnetization of quantum dots is discussed in terms of a relatively
simple but exactly solvable model Hamiltonian. The model predicts oscillations
in spin polarization as a function of dot radius for a fixed electron density.
These oscillations in magnetization are shown to yield distinct signature in
the momentum density of the electron gas, suggesting the usefulness of momentum
resolved spectroscopies for investigating the magnetization of dot systems. We
also present variational quantum Monte Carlo calculations on a square dot
containing 12 electrons in order to gain insight into correlation effects on
the interactions between like and unlike spins in a quantum dot.Comment: 6 pages, 4 figure
A natural orbital method for the electron momentum distribution in matter
A variational method for many electron system is applied to momentum
distribution calculations. The method uses a generating two-electron geminal
and the amplitudes of the occupancies of one particle natural orbitals as
variational parameters. It introduces correlation effects beyond the free
fermion nodal structure.Comment: 3 pages, Latex, revised paper with new reference
Electronic structure of rectangular quantum dots
We study the ground state properties of rectangular quantum dots by using the
spin-density-functional theory and quantum Monte Carlo methods. The dot
geometry is determined by an infinite hard-wall potential to enable comparison
to manufactured, rectangular-shaped quantum dots. We show that the electronic
structure is very sensitive to the deformation, and at realistic sizes the
non-interacting picture determines the general behavior. However, close to the
degenerate points where Hund's rule applies, we find spin-density-wave-like
solutions bracketing the partially polarized states. In the
quasi-one-dimensional limit we find permanent charge-density waves, and at a
sufficiently large deformation or low density, there are strongly localized
stable states with a broken spin-symmetry.Comment: 8 pages, 9 figures, submitted to PR
Calculation of positron states and annihilation in solids: A density-gradient-correction scheme
The generalized gradient correction method for positron-electron correlation effects in solids [B. Barbiellini et al., Phys. Rev. B 51, 7341 (1995)] is applied in several test cases. The positron lifetime, energetics, and momentum distribution of the annihilating electron-positron pairs are considered. The comparison with experiments shows systematic improvement in the predictive power of the theory compared to the local-density approximation results for positron states and annihilation characteristics.Peer reviewe
Generalised Lyndon-Schützenberger Equations
We fully characterise the solutions of the generalised Lyndon-Schützenberger word equations , where for all , for all , for all , and is an antimorphic involution. More precisely, we show for which , , and such an equation has only -periodic solutions, i.e., , , and are in for some word , closing an open problem by Czeizler et al. (2011)
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