Search results for "Van der Waals force"
showing 10 items of 170 documents
The influence of disorder on the exciton spectra in two-dimensional structures
2019
We study the role of disorder in the exciton spectra in two-dimensional (2D) semiconductors. These can be heterostructures, thin films and multilayers (so-called van der Waals structures) of organometallic perovskites, transition metal dichalcogenides and other semiconductors for optoelectronic applications. We model the disorder by introduction of a fractional Laplacian (with Le´vy index m, defining the degree of disorder) to the Scro¨dinger equation with 2D Coulomb potential. Combining analytical and numerical methods, we observe that the exciton exists only for m 4 1, while the point m = 1 (strongest disorder) corresponds to the exciton collapse. We show also that in the fractional (diso…
Controlling the interactions of a few cold Rb Rydberg atoms by radiofrequency-assisted F\"orster resonances
2014
Long-range interactions between cold Rydberg atoms, which are used in many important applications, can be enhanced using F\"orster resonances between collective many-body states controlled by an external electric field. Here we report on the first experimental observation of highly-resolved radio-frequency-assisted F\"orster resonances in a few cold Rb Rydberg atoms. We also observed radio-frequency-induced F\"orster resonances which cannot be tuned by a dc electric field. They imply an efficient transition from van der Waals to resonant dipole-dipole interaction due to Floquet sidebands of Rydberg levels appearing in the rf-field. This method can be applied to enhance the interactions of a…
Full configuration interaction calculation of Be3.
2004
The full configuration interaction (FCI) study of the ground state of the neutral beryllium trimer has been performed using an atomic natural orbitals [3s2p1d] basis set. Both triangular and linear structures have been considered for the Be(3) cluster. The optimal geometry for the equilateral triangle has been calculated. The potential energy cut sections along the normal a(1)(') mode and one of the components of the e(') mode have then been studied. The FCI symmetric atomization potential of the linear cluster is also reported. It shows a secondary van der Waals minimum at a long bond distance. All singular points in the potential energy curves are characterized. Other properties, like dis…
van der Waals Interaction Energy Between Two Atoms Moving With Uniform Acceleration
2013
We consider the interatomic van der Waals interaction energy between two neutral ground-state atoms moving in the vacuum space with the same uniform acceleration. We assume the acceleration orthogonal to their separation, so that their mutual distance remains constant. Using a model for the van der Waals dispersion interaction based on the interaction between the instantaneous atomic dipole moments, which are induced and correlated by the zero-point field fluctuations, we evaluate the interaction energy between the two accelerating atoms in terms of quantities expressed in the laboratory reference frame. We find that the dependence of the van der Waals interaction between the atoms from the…
Microscopic approach to the kinetics of pattern formation of charged molecules on surfaces.
2010
A microscopic formalism based on computing many-particle densities is applied to the analysis of the diffusion-controlled kinetics of pattern formation in oppositely charged molecules on surfaces or adsorbed at interfaces with competing long-range Coulomb and short-range Lennard-Jones interactions. Particular attention is paid to the proper molecular treatment of energetic interactions driving pattern formation in inhomogeneous systems. The reverse Monte Carlo method is used to visualize the spatial molecular distribution based on the calculated radial distribution functions (joint correlation functions). We show the formation of charge domains for certain combinations of temperature and dy…
Monte Carlo simulation of crystalline polyethylene
1996
Abstract We consider here the problem of constructing an efficient algorithm for a classical Monte Carlo simulation of crystalline polyethylene with unconstrained bond lengths and angles. This macromolecular crystal presents a particular example of a system with many different energy scales, ranging from soft ones represented by nonbonded van der Waals interactions, to stiff ones, represented in particular by bond stretching. A proper sampling of all the energy scales poses a problem and it is shown that a standard Metropolis algorithm employing just local moves is not very efficient at low temperatures. As a solution it is proposed to employ also global moves consisting of displacements of…
Mott scattering as a probe of long range QCD effects
1994
We investigate the possibility of using the Mott scattering between identical nuclei to assess the existence of long range QCD effects, e.g., a color van der Waals interaction, as suggested recently. We show that the inclusion of atomic effects is very important and should be considered in order to extract limits on the strength of the color van der Waals force. We compare our calculations with the analysis of a recent heavy ion experiment.
Discriminating short-range from van der Waals forces using total force data in noncontact atomic force microscopy
2014
Noncontact atomic force microscopy (NC-AFM) features the measurement of forces with highest spatial resolution and sensitivity, resolving forces of the order of pico-Newtons with submolecular resolution. However, the measured total force is a mixture composed of various interactions. While some interactions such as electrostatic or magnetic forces can be excluded by a careful design of the experiment, the subtraction of van der Waals forces, which mainly originate from London dispersion interactions between the macroscopic tip shank and the bulk sample, remains a challenge. We present the determination of the inherently present van der Waals forces in total interaction force data from fitti…
Geometry and time scale of the rotational dynamics in supercooled toluene
1998
Multidimensional deuteron NMR provides powerful tools for studying molecular reorientation in supercooled liquids. We present results on selectively deuterated toluene-${d}_{5},$ which may be one of the molecularly most simple van der Waals glass formers. From two-time correlation functions the time scale of reorientation was obtained slightly above the calorimetric glass transition temperature. The applied stimulated echo method provides a geometry parameter that, in analogy to $q$-dependent scattering experiments, allows one to investigate the geometry of the elementary rotational process. Continuous time random walk computer simulations were used for the interpretation of the data. It is…
Dynamical Casimir-Polder energy between an excited- and a ground-state atom.
2004
We consider the Casimir-Polder interaction between two atoms, one in the ground state and the other in its excited state. The interaction is time-dependent for this system, because of the dynamical self-dressing and the spontaneous decay of the excited atom. We calculate the dynamical Casimir-Polder potential between the two atoms using an effective Hamiltonian approach. The results obtained and their physical meaning are discussed and compared with previous results based on a time-independent approach which uses a non-normalizable dressed state for the excited atom.