35 research outputs found
Thermal dissociation of dipositronium: path integral Monte Carlo approach
Path integral Monte Carlo simulation of the dipositronium "molecule" Ps
reveals its surprising thermal instability. Although, the binding energy is
eV, due to the strong temperature dependence of its free energy
Ps dissociates, or does not form, above K, except for high
densities where a small fraction of molecules are in equilibrium with Ps atoms.
This prediction is consistent with the recently reported first observation of
stable Ps molecules by Cassidy & Mills Jr., Nature {\bf 449}, 195 (07), and
Phys.Rev.Lett. {\bf 100}, 013401 (08); at temperatures below 1000 K. The
relatively sharp transition from molecular to atomic equilibrium, that we find,
remains to be experimentally verified. To shed light on the origin of the large
entropy factor in free energy we analyze the nature of interatomic interactions
of these strongly correlated quantum particles. The conventional diatomic
potential curve is given by the van der Waals interaction at large distances,
but due to the correlations and high delocalization of constituent particles
the concept of potential curve becomes ambiguous at short atomic distances.Comment: Submitted to the Physical Review Letter
Finite temperature quantum statistics of H molecular ion
Full quantum statistical simulation of the five-particle system H
has been carried out using the path integral Monte Carlo method. Structure and
energetics is evaluated as a function of temperature up to the thermal
dissociation limit. The weakly density dependent dissociation temperature is
found to be around K. Contributions from the quantum dynamics and
thermal motion are sorted out by comparing differences between simulations with
quantum and classical nuclei. The essential role of the quantum description of
the protons is established.Comment: submitted to the Journal of Chemical Physic
Few-body reference data for multicomponent formalisms: Light nuclei molecules
We present full quantum statistical energetics of some electron-light nuclei
systems. This is accomplished with the path integral Monte Carlo method. The
effects on energetics arising from the change in the nuclear mass are studied.
The obtained results may serve as reference data for the multicomponent density
functional theory calculations of light nuclei system. In addition, the results
reported here will enable better fitting of todays electron-nuclear energy
functionals, for which the description of light nuclei is most challenging, in
particular
Path Integrals: From Quantum Mechanics to Photonics
The path integral formulation of quantum mechanics, i.e., the idea that the
evolution of a quantum system is determined as a sum over all the possible
trajectories that would take the system from the initial to its final state of
its dynamical evolution, is perhaps the most elegant and universal framework
developed in theoretical physics, second only to the Standard Model of particle
physics. In this tutorial, we retrace the steps that led to the creation of
such a remarkable framework, discuss its foundations, and present some of the
classical examples of problems that can be solved using the path integral
formalism, as a way to introduce the readers to the topic, and help them get
familiar with the formalism. Then, we focus our attention on the use of path
integrals in optics and photonics, and discuss in detail how they have been
used in the past to approach several problems, ranging from the propagation of
light in inhomogeneous media, to parametric amplification, and quantum
nonlinear optics in arbitrary media. To complement this, we also briefly
present the Path Integral Monte Carlo (PIMC) method, as a valuable
computational resource for condensed matter physics, and discuss its potential
applications and advantages if used in photonics
Effects of solar irradiation on thermally driven CO2 methanation using Ni/CeO2-based catalyst
Utilization of the renewable energy sources is one of the main challenges in the state-of-the-art technologies for CO2 recycling. Here we have taken advantage of the solar light harvesting in the thermocatalytic approach to carbon dioxide methanation. The large-surface-area Ni/CeO2 catalyst produced by a scalable low-cost method was characterized and tested in the dark and under solar light irradiation conditions. Light-assisted CO2 con-version experiments as well as in-situ DRIFT spectrometry, performed at different illumination intensities, have revealed a dual effect of the incident photons on the catalytic properties of the two-component Ni/CeO2 catalyst. On the one hand, absorbed photons induce a localized surface plasmon resonance in the Ni nanoparticles fol-lowed by dissipation of the heat to the oxide matrix. On the other hand, the illumination activates the photo-catalytic properties of the CeO2 support, which leads to an increase in the concentration of the intermediates being precursor for methane production. Analysis of the methane production at different temperatures and illumination conditions has shown that the methanation reaction in our case is controlled by a photothermally- activated process. The used approach has allowed us to increase the reaction rate up to 2.4 times and conse-quently to decrease the power consumption by 20 % under solar illumination, thus replacing the conventional thermal activation of the reaction with a green energy source