Possibility Of Energy Exchange Research Articles

Vibrational Excitation of H2 Scattering from Cu(111): Effects of Surface Temperature and of Allowing Energy Exchange with the Surface

In scattering of H2 from Cu(111), vibrational excitation has so far defied an accurate theoretical description. To expose the causes of the large discrepancies with experiment, we investigate how the feature due to vibrational excitation (the “gain peak”) in the simulated time-of-flight spectrum of (v = 1, j = 3) H2 scattering from Cu(111) depends on the surface temperature (Ts) and the possibility of energy exchange with surface phonons and electron–hole pairs (ehp’s). Quasi-classical dynamics calculations are performed on the basis of accurate semiempirical density functionals for the interaction with H2 + Cu(111). The methods used include the quasi-classical trajectory method within the Born–Oppenheimer static surface model, the generalized Langevin oscillator (GLO) method incorporating energy transfer to surface phonons, the GLO + friction (GLO+F) method also incorporating energy exchange with ehp’s, and ab initio molecular dynamics with electronic friction (AIMDEF). Of the quasi-classical methods tested, comparison with AIMDEF suggests that the GLO+F method is accurate enough to describe vibrational excitation as measured in the experiments. The GLO+F calculations also suggest that the promoting effect of raising Ts on the measured vibrational excitation is due to an electronically nonadiabatic mechanism. However, by itself, enabling energy exchange with the surface by modeling surface phonons and ehp’s leads to reduced vibrational excitation, further decreasing the agreement with experiment. The simulated gain peak is quite sensitive to energy shifts in calculated vibrational excitation probabilities and to shifts in a specific experimental parameter (the chopper opening time). While the GLO+F calculations allow important qualitative conclusions, comparison to quantum dynamics results suggests that, with the quasi-classical way of describing nuclear motion and the present box quantization method for assigning the final vibrational state, the gain peak is not yet described with quantitative accuracy. Ways in which this problem might be resolved in the future are discussed.

Energy Exchange Between the Discrete Breathers in Graphane

Discrete breathers in graphane (fully hydrogenated graphene) are studied by the molecular dynamics method. It has previously been demonstrated that in graphane, there are discrete breathers in the form of single hydrogen atoms oscillating with the big amplitude in the direction perpendicular to the graphane plane with a frequency lying in the bandgap of the phonon spectrum. In this work, the possibility of the existence of longlived clusters of discrete breathers of different configurations is shown, their properties are studied, and the possibility of energy exchange between the discrete breathers in the cluster is demonstrated. These results are important for the discussion of physical processes occurring during dehydrogenation of graphane at high temperatures, which, in turn, is of great importance for the development of the hydrogen storage and transport devices based on sp2-carbon materials.

A Similarity on Energy Exchange Between Resonance and Synchronization

This research focuses on a possibility to scavenge energy from fluid flow including turbulence. Based on turbulent mechanics, energy scavenging devices are expected to have nonlinear characteristics to accept wide-band-spectrum power distributed in turbulence. A magnetoelastic beam is adopted as one of candidates of energy scavenging devices. The magnetoelastic beam is excited in a nonlinear magnetic field formed by two magnets. In this paper, we estimate the possibility of energy exchange at synchronization as the scavenging mechanism, with considering the similarity to resonance.

Improved importance sampling distribution for rate constant calculation

An efficient method to compute the thermal rate constant for rare events within the correlation function C(t) approach is presented. This method, which is based on a modification of the sampling function used to evaluate the dynamical correlation function C(t), can be applied to high-dimensional systems having a rough energy landscape without previous knowledge on the transition states location. In this work, the sampling of a Boltzmann-like distribution for the linear momenta with a lower inverse temperature (beta(*)=1/kT(*)) than the correct one (beta=1/kT) is proposed as a way to increase the number of reactive trajectories. The mismatch between the beta(*) and beta distributions is then corrected by a reweighting procedure which allows one to obtain the exact correlation function C(t). The efficiency of this scheme in computing the rate of a particle jumping across the barrier of a simple 2D double well potential is improved by a factor 4-25 depending on the relative value of the original beta and modified beta(*) temperatures. When merged with the "puddle potential" method [S. A. Corcelli, J. A. Rohman, and J. C. Tully, J. Chem. Phys., 118, 1085 (2003)], the new importance sampling function improves the efficiency of the correlation function approach by a factor 16-800 with respect to the unbiased sampling. To test the method in a more challenging case, the previous model system was extended by adding six harmonically restrained particles, each one interacting with the diffusing particle. This model introduces both the possibility of energy exchange and a rougher energy landscape. The new sampling function alone is found to produce an improvement in efficiency of, at least, an order of magnitude when compared with the unbiased case; when merged with the puddle potential method, a 400-fold saving in computer time is found.

Dynamic control of electronic states in a double quantum dot under weak dissipation conditions

The problem of the time evolution of an electron wave packet in a symmetric double quantum dot under the action of a strong alternating electric field and a slowly varying bias voltage is solved theoretically under the conditions when the electron subsystem can transfer its energy to a single resonator mode. It is shown that the possibility of energy exchange between the electron subsystem and the resonator does not hamper the formation of stable electronic states localized in the left or right quantum dot (i.e., polarized states possessing a positive or negative dipole moment). An adiabatic change in the bias voltage may alter the direction of the dipole moment of the given state (which corresponds to an electron transition from one quantum dot to the other).

Propagation of radiation in a medium with complex matrix elements

We consider here the propagation of the radiation intensity, represented by Tr {ϱa k † a k }, in a medium made up of electrons with non-overlapping wave functions bound atN discrete points. They are bound by a local potential and are subject to a constant external magnetic field. It is found using perturbation theory to fourth order in the matrix elements that if the matrix elements of the electron are real the intensity for single-mode propagation is unaffected by the unperturbed fourth-order coherence function, Tr {ϱa k + a k Emphasis>† a k a k }. If the elements are complex, however, the intensity is dependent on this function. This result is found in the absence of absorption or stimulated emission as commonly defined and raises the possibility of energy exchange between the radiation field and the static external field.