index - Théorie Accéder directement au contenu

Derniers dépôts, tout type de documents

In this article, we investigate the optical response of a duplicated two-level atomic medium submitted to a strong stationnary control field and a weak co-propagating probe field, orthogonally polarized to each other. We show that both reflected and transmitted components of the probe may be absorbed and amplified. Moreover, for low optical depths, reflection and transmission factors are controlled by the relative phase between control and probe fields, which makes the configuration we present here promising for the development of optical devices, such as phase-controlled switches.

Continuer la lecture Share

The sinking of alkali cations in superfluid 4He nanodroplets is investigated theoretically using liquid 4He time-dependent density functional theory at zero temperature. The simulations illustrate the dynamics of the buildup of the first solvation shell around the ions. The number of helium atoms in this shell is found to linearly increase with time during the first stages of the dynamics. This points to a Poissonian capture process, as concluded in the work of Albrechtsen et al. on the primary steps of Na+ solvation in helium droplets [Albrechtsen et al., Nature 623, 319 (2023)]. The energy dissipation rate by helium atom ejection is found to be quite similar between all alkalis, the main difference being a larger energy dissipated per atom for the lighter alkalis at the beginning of the dynamics. In addition, the number of helium atoms in the first solvation shell is found to be lower at the end of the dynamics than at equilibrium for both Li+ and Na+, pointing to a kinetic rather than thermodynamical control of the snowball size for small and strongly attractive ions.

Continuer la lecture Share

The accurate description of an atom or molecule colliding with a metal surface remains challenging. Several strategies have been performed over the past decades to include in a Langevin dynamics the energy transfer related to electron-hole pair excitations in a phenomenological way through a friction contribution. We report the adaptation of two schemes previously developed in the litterature to couple the electronic friction dynamics with the Density-Functional based Tight-Binding (DFTB) approach. The first scheme relies on an electronic isotropic friction coefficient determined from the local electronic density (Local Density Friction Approximation or LDFA). In the second one, a tensorial friction is generated from the non-adiabatic couplings of the ground electronic state with the single electron-hole excitations (Electron Tensor Friction Approximation or ETFA). New DFTB parameterization provides potential energy curves in good agreement with first-principle Density-Functional Theory (DFT) energy calculations for selected pathways of hydrogen atom adsorbing onto the (100) silver surface or penetrating subsurface. Preliminary DFTB/Langevin dynamics simulations are presented for hydrogen atom scattering from the (100) silver surface and energy loss timescales are characterized.

Continuer la lecture Share

Interactions between molecular hydrogen and ions are of interest in cluster science, astrochemistry and hydrogen storage. In dynamical simulations, H2 molecules are usually modelled as point particles, an approximation that can fail for anisotropic interactions. Here, we apply an adiabatic separation of the H2 rotational motion to build effective pseudoatom-ion potentials and in turn study the properties of (H2)nNa+/Cl− clusters. These interaction potentials are based on high-level ab initio calculations and Improved Lennard-Jones parametrizations, while the subsequent dynamics has been performed by quantum Monte Carlo calculations. By comparisons with simulations explicitly describing the molecular rotations, it is concluded that the present adiabatic model is very adequate. Interestingly, we find differences in the cluster stabilities and coordination shells depending on the spin isomer considered (para- or ortho-H2), especially for the anionic clusters.

Continuer la lecture Share

Recent experiments have shown that translational energy loss is mainly mediated by electron–hole pair excitations for hydrogen atoms impinging on clean metallic surfaces. Inspired by these studies, quasi-classical trajectory simulations are here performed to investigate the energy transfer after scattering of hydrogen atoms off clean and hydrogen-covered tungsten (100) surfaces. The present theoretical approach examines the coverage effect of the preadsorbed hydrogen atoms, as was done recently for the (110) crystallographic plane in (J Phys Chem C 125:14075, 2021). As suggested, scattering can be described in terms of three different dynamical mechanisms, the contribution of which changes with coverage, which allow to rationalize the shape of the energy loss spectra.

Continuer la lecture Share

Sujets

Density functional theory DENSITY MODEL Non-equilibrium Green's function Diels-Alder reaction Tetrathiafulvalene Dynamique non-adiabatique Collisions ultra froides Muonic hydrogen Ultrashort pulses Half revival ALGORITHM Dissipative dynamics Clusters COHERENT CONTROL Effets inélastiques Contrôle cohérent AR Transport électronique Electron-surface collision CONICAL INTERSECTION Deformation CHEMICAL-REACTIONS Dynamique quantique Cope rearrangement Calcium Propagation effects DISSIPATION ENTROPY Close-coupling STATE Transitions non-adiabatiques MCTDH Anisotropy ELECTRON DYNAMICS Superfluid helium nanodroplets DEPENDENT SCHRODINGER-EQUATION Electric field Ab-initio Photophysics QUANTUM OPTIMAL-CONTROL ENERGY Dynamics Dissipation CLASSICAL TRAJECTORY METHOD Extra dimension Cluster WAVE-PACKET DYNAMICS Rydberg atoms Effets isotopiques Coulomb presssure Cesium DIFFERENTIAL CROSS-SECTIONS DRIVEN Classical trajectory Dynamique moléculaire quantique Drops COMPLEX ABSORBING POTENTIALS DEMO ELECTRON-NUCLEAR DYNAMICS Quantum dynamics Effets transitoires Fonction de Green hors-équilibre Wave packet interferences CAVITY ELECTRONIC BUBBLE FORMATION Ab initio calculations Composés organiques à valence mixte Dissipative quantum methods Theory Anharmonicity Casimir effect Agrégats Dynamique mixte classique Théorie de la fonctionnelle de la densité Slow light Dark energy 4He-TDDFT simulation Cosmological constant ENTANGLEMENT Atomic collisions DYNAMICS Coherent control Atom Atomic clusters Ejection Cryptochrome Molecules Bohmian trajectories Atomic scattering from surfaces Coordonnées hypersphériques elliptiques Collisions des atomes Alkali-halide Electronic Structure Electronic transport inelastic effects COLLISION ENERGY Electron transfer Collision frequency Effets de propagation DFTB

Statistiques

Nombre de fichiers déposés

67

Nombre de notices déposées

168