82 research outputs found
Pair-correlation properties and momentum distribution of finite number of interacting trapped bosons in three dimension
We study the ground state pair-correlation properties of a weakly interacting
trapped Bose gas in three dimension by using a correlated many-body method. Use
of the van der Waals interaction potential and an external trapping potential
shows realistic features. We also test the validity of shape-independent
approximation in the calculation of correlation properties.Comment: Accepted for publication in The Journal of Chemical Physic
Stability of attractive bosonic cloud with van der Waals interaction
We investigate the structure and stability of Bose-Einstein condensate of
Li atoms with realistic van der Waals interaction by using the potential
harmonic expansion method. Besides the known low-density metastable solution
with contact delta function interaction, we find a stable branch at a higher
density which corresponds to the formation of an atomic cluster. Comparison
with the results of non-local effective interaction is also presented. We
analyze the effect of trap size on the transition between the two branches of
solutions. We also compute the loss rate of a Bose condensate due to two- and
three-body collisions.Comment: 9 pages, 5 figure
Destruction of attractive bosonic cloud due to high spatial coherence in tight trap
We study coherence of a trapped bosonic cloud with attractive finite-range
interaction in a tight harmonic trap. One-body density and pair-distribution
function in the ground state for different trap sizes are calculated. We also
calculate healing length and the correlation length which signify the presence
of high spatial coherence in a very tight trap leading to the destruction of
the condensate for a fixed particle number. This is in marked variance with the
usual collapse of the attractive metastable condensate when N > Ncr . Thus we
investigate the critical frequency and critical size of the trap for the
existence of attractive Bose-Einstein condensation. The finite-range
interaction gives a nonlocal effect in the effective many-body potential, and
we observe a high-density stable branch besides the known metastable branch.
Moreover, the new branch shows universal behavior even in the very tight trap
Continuous transition of social efficiencies in the stochastic strategy Minority Game
We show that in a variant of the Minority Game problem, the agents can reach
a state of maximum social efficiency, where the fluctuation between the two
choices is minimum, by following a simple stochastic strategy. By imagining a
social scenario where the agents can only guess about the number of excess
people in the majority, we show that as long as the guess value is sufficiently
close to the reality, the system can reach a state of full efficiency or
minimum fluctuation. A continuous transition to less efficient condition is
observed when the guess value becomes worse. Hence, people can optimize their
guess value for excess population to optimize the period of being in the
majority state. We also consider the situation where a finite fraction of
agents always decide completely randomly (random trader) as opposed to the rest
of the population that follow a certain strategy (chartist). For a single
random trader the system becomes fully efficient with majority-minority
crossover occurring every two-days interval on average. For just two random
traders, all the agents have equal gain with arbitrarily small fluctuations.Comment: 8 pages, 6 fig
Time-dependent density functional theory calculation of van der Waals coefficient of sodium clusters
In this paper we employ all-electron \textit{ab-initio} time-dependent
density functional theory based method to calculate the long range
dipole-dipole dispersion coefficient (van der Waals coefficient) of
sodium atom clusters containing even number of atoms ranging from 2 to 20
atoms. The dispersion coefficients are obtained via Casimir-Polder relation.
The calculations are carried out with two different exchange-correlation
potentials: (i) the asymptotically correct statistical average of orbital
potential (SAOP) and (ii) Vosko-Wilk-Nusair representation of
exchange-correlation potential within local density approximation. A comparison
with the other theoretical results has been performed. We also present the
results for the static polarizabilities of sodium clusters and also compare
them with other theoretical and experimental results. These comparisons reveal
that the SAOP results for C_{6} and static polarizability are quite accurate
and very close to the experimental results. We examine the relationship between
volume of the cluster and van der Waals coefficient and find that to a very
high degree of correlation C_{6} scales as square of the volume. We also
present the results for van der Waals coefficient corresponding to cluster-Ar
atom and cluster-N_{2} molecule interactions.Comment: 22 pages including 6 figures. To be published in Journal of Chemical
Physic
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