C4分子在激光场中的密度泛函理论研究

采用含时局域密度近似与分子动力学相结合的方法计算了C4分子的光学吸收谱及它在激光场中的响应。研究表明,在激光场中C4分子的诱导偶极矩与电离之间有着直接的联系,最外层电子对电离的贡献最大。此外,通过对激光的极化方向与C4分子的激发的关系的研究表明,x方向的激光场唯一的激发起C4分子x方向的偶极矩,电离增强而且离子的振动增强。     

C4分子在激光场中的密度泛函理论研究

采用含时局域密度近似与分子动力学相结合的方法计算了C4分子的光学吸收谱及它在激光场中的响应.研究表明,在激光场中C4分子的诱导偶极矩与电离之间有着直接的联系,最外层电子对电离的贡献最大.此外,通过对激光的极化方向与C4分子的激发的关系的研究表明,x方向的激光场唯一的激发起C4分子x方向的偶极矩,电离增强而且离子的振动增强.     

Impact of ionic motion on ionization of metal clusters under intense laser pulses

We discuss the impact of ionic motion on ionization of metal clusters subject to intense laser pulses in a microscopic approach. We show that for long enough pulses, ionic expansion can drive the system into resonance with the electronic plasmon resonance, which leads to a strongly enhanced ionization.     

DFT studies of ionic vibrations in Na clusters

We use time-dependent density functional theory coupled to molecular dynamics for ionic motion to compute the spectra of ionic vibrations in small Na clusters. Comparison with results from the distance dependent tight-binding approach shows good agreement between these two very different methods. We discuss the evolution of the spectra with cluster size and charge and the impact of ionic vibrations on the optical response. Received 23 July 2001 / Received in final form 5 July 2002 Published online 8 October 2002 RID="a" ID="a"e-mail: suraud@irsamc.ups-tlse.fr     

Coupling of core excitation and single-particle motion in odd-a-nuclei

A physical fractional parentage expansion is presented which can be used to treat the coupling of single-particle and core motion in terms of the physical eigenstates of the core. The antisymmetry requirement is formulated in a subsidiary condition which allows diagonalization of the coupling Hamiltonian in the product space of the core and the extra-core particle. Restriction to a subset of core excitations leads to only approximate fulfillment of the subsidiary condition. The usefulness of the method is tested in the quasi-spin model.     

Structural transitions in small nickel clusters

The processes of a thermal impact on Ni nanoclusters with a radius of up to 0.8 nm have been studied by means of molecular dynamics with the use of a tight-binding potential. The simulation indicates that the structural transition from the initial fcc phase to the icosahedral modification occurs under the influence of temperature. The transition temperature is shifted towards the cluster melting temperature with an increase in the cluster size. A similar behavior has been observed for copper and gold nanoparticles. A conclusion has been drawn that 200–250 atoms is presumably the limiting size of a metallic cluster, below which the initial fcc modification cannot be kept under realistic industrial conditions. The adequacy of the results is checked in the computer experiments with Lennard-Jones nanoparticles. The results for the Lennard-Jones and metallic nanoparticles have been shown to agree with each other.     

Defect studies in small CdTe clusters

We study Cd vacancy formation in prototype stoichiometric and non-stoichiometric CdTe clusters with and without passivation. For certain clusters like Cd₁₃Te₁₆, vacancy leads to severe distortion of the geometry due to propagation of defect. Annealing of the vacancy out of the cluster is observed in all unpassivated clusters. Passivated clusters retain their initial geometry and vacancy induced structural distortions are not seen in these clusters since the defect gets localized. Vacancy also induces intragap states. However, it was observed that the passivation of the dangling bonds created by the vacancy removes the intragap states. In an attempt to have CdTe clusters with extrinsic carriers, we substituted a Cd atom by its adjacent atoms Pd/Ag/In/Sn in these CdTe clusters. Substitutional doping of Cd by metal atoms increases the stability of unpassivated clusters. For certain clusters, metal atom doping leads to a half-metallic character. Pd/Ag-doped clusters are p-type semiconductors whereas In-doped clusters are n-type semiconductors. Sn doping in these clusters does not result in n-type semiconductors.     

Structural transition in small gas-like clusters

We propose a model, which is an alternative to the droplet model and presumes that the number of bonds between the atoms is a minimum, to describe highly excited clusters containing a small number of atoms. It is shown that at sufficiently high temperatures such a structure, which has the form of a system of spontaneously appearing chains of atoms (virtual chains),is realized with a greater probability than the close-packed structure. Analytic estimates are supported by the results of numerical molecular-dynamics simulations. Zh. éksp. Teor. Fiz. 113, 181–190 (January 1998)     

Comments on small superconducting clusters

The feasibility of an experimental study of small superconducting clusters (SC) is analyzed. Critical sizes for SC are calculated. Oscillations of the energy gap and the diamagnetic susceptibility of SC are considered.     

Laser induced excitation transfer in helium glow discharge

Some experimental results on the temporal decay of the fluorescence induced by a resonant laser pulse excitation focused onto a helium gas discharge are presented. In particular, excitation transfer between singlet-singlet and singlet- triplet sub-levels has been studied when 2¹ S → 3¹ P and 2¹ P → 4¹ D transitions of He I are optically pumped.