4,196 research outputs found
Energy and structure of dilute hard- and soft-sphere gases
The energy and structure of dilute hard- and soft-sphere Bose gases are
systematically studied in the framework of several many-body approaches, as the
variational correlated theory, the Bogoliubov model and the uniform limit
approximation, valid in the weak interaction regime. When possible, the results
are compared with the exact diffusion Monte Carlo ones. A Jastrow type
correlation provides a good description of the systems, both hard- and
soft-spheres, if the hypernetted chain energy functional is freely minimized
and the resulting Euler equation is solved. The study of the soft-spheres
potentials confirms the appearance of a dependence of the energy on the shape
of the potential at gas paremeter values of . For quantities
other than the energy, such as the radial distribution functions and the
momentum distributions, the dependence appears at any value of . The
occurrence of a maximum in the radial distribution function, in the momentum
distribution and in the excitation spectrum is a natural effect of the
correlations when increases. The asymptotic behaviors of the functions
characterizing the structure of the systems are also investigated. The uniform
limit approach results very easy to implement and provides a good description
of the soft-sphere gas. Its reliability improves when the interaction weakens.Comment: Accepted in Phys. Rev.
Energy and Structure of Hard-Sphere Bose Gases in three and two dimensions
The energy and structure of dilute gases of hard spheres in three dimensions
is discussed, together with some aspects of the corresponding 2D systems. A
variational approach in the framework of the Hypernetted Chain Equations (HNC)
is used starting from a Jastrow wavefunction that is optimized to produce the
best two--body correlation factor with the appropriate long range. Relevant
quantities describing static properties of the system are studied as a function
of the gas parameter where , and are the density,
--wave scattering length of the potential and dimensionality of the space,
respectively. The occurrence of a maximum in the radial distribution function
and in the momentum distribution is a natural effect of the correlations when
increases. Some aspects of the asymptotic behavior of the functions
characterizing the structure of the systems are also investigated.Comment: Proceedings of the QFS2004 conference in Trento. To appear in JLT
Coherent and Incoherent Dynamic Structure Function of the Free Fermi Gas
A detailed calculation of the coherent and incoherent dynamic structure
functions of the free Fermi gas, starting from their expressions in terms of
the one- and semi-diagonal two-body density matrices, is derived and discussed.
Their behavior and evolution with the momentum transfer is analyzed, and
particular attention is devoted to the contributions that both functions
present at negative energies. Finally, an analysis of the energy weighted sum
rules satisfied by both responses is also performed. Despite of the simplicity
of the model, some of the conclusions can be extended to realistic systems.Comment: LaTeX, 3 figure
Recommended from our members
Formalising Engineering Judgement on Software Dependability via Belief Networks
Dichloromethylation of enones by carbon nitride photocatalysis
Small organic radicals are ubiquitous intermediates in photocatalysis and are used in organic synthesis to install functional groups and to tune electronic properties and pharmacokinetic parameters of the final molecule. Development of new methods to generate small organic radicals with added functionality can further extend the utility of photocatalysis for synthetic needs. Herein, we present a method to generate dichloromethyl radicals from chloroform using a heterogeneous potassium poly(heptazine imide) (K-PHI) photocatalyst under visible light irradiation for C1-extension of the enone backbone. The method is applied on 15 enones, with γ,γ-dichloroketones yields of 18–89%. Due to negative zeta-potential (−40 mV) and small particle size (100 nm) K-PHI suspension is used in quasi-homogeneous flow-photoreactor increasing the productivity by 19 times compared to the batch approach. The resulting γ,γ-dichloroketones, are used as bifunctional building blocks to access value-added organic compounds such as substituted furans and pyrroles
Single-particle vs. pair superfluidity in a bilayer system of dipolar bosons
We consider the ground state of a bilayer system of dipolar bosons, where
dipoles are oriented by an external field in the direction perpendicular to the
parallel planes. Quantum Monte Carlo methods are used to calculate the
ground-state energy, the one-body and two-body density matrix, and the
superfluid response as a function of the separation between layers. We find
that by decreasing the interlayer distance for fixed value of the strength of
the dipolar interaction, the system undergoes a quantum phase transition from a
single-particle to a pair superfluid. The single-particle superfluid is
characterized by a finite value of both the atomic condensate and the
super-counterfluid density. The pair superfluid phase is found to be stable
against formation of many-body cluster states and features a gap in the
spectrum of elementary excitations.Comment: 4 figure
- …