Atomic clusters dynamics

I Andricioaei, JE Straub. On Monte Carlo and molecular dynamics methods inspired by Tsallis statistics Methodology, optimization, and application to atomic clusters. J Chem Phys 107 9117-9124, 1997. 

KD Ball, RS Beii y, RE Kunz, E-Y Li, A Proykova, DJ Wales. Erom topographies to dynamics of multidimensional potential energy surfaces of atomic clusters. Science 271 963-966, 1996. RS Berry, N Elmaci, JP Rose, B Vekhter. Linking topography of its potential surface with the dynamics of folding of a protein model. Proc Natl Acad Sci USA 94 9520-9524, 1997. Z Guo, D Thii-umalai. J Mol Biol 263 323-343, 1996. 

In 1985 Car and Parrinello invented a method [111-113] in which molecular dynamics (MD) methods are combined with first-principles computations such that the interatomic forces due to the electronic degrees of freedom are computed by density functional theory [114-116] and the statistical properties by the MD method. This method and related ab initio simulations have been successfully applied to carbon [117], silicon [118-120], copper [121], surface reconstruction [122-128], atomic clusters [129-133], molecular crystals [134], the epitaxial growth of metals [135-140], and many other systems for a review see Ref. 113. 

Due to particles extrusion, crystal lattice deformation expands to the adjacent area, though the deformation strength reduces gradually (Figs. 10(a)-10(other hand, after impacting, the particle may retain to plow the surface for a short distance to exhaust the kinetic energy of the particle. As a result, parts of the free atoms break apart from the substrate and pile up as atom clusters before the particle. The observation is consistent with results of molecular dynamics simulation of the nanometric cutting of silicon [15] and collision of the nanoparticle with the solid surface [16]. 

SRPA has been already applied for atomic nuclei and clusters, both spherical and deformed. To study dynamics of valence electrons in atomic clusters, the Konh-Sham functional [14,15]was exploited [7,8,16,17], in some cases together with pseudopotential and pseudo-Hamiltonian schemes [16]. Excellent agreement with the experimental data [18] for the dipole plasmon was obtained. Quite recently SRPA was used to demonstrate a non-trivial interplay between Landau fragmentation, deformation splitting and shape isomers in forming a profile of the dipole plasmon in deformed clusters [17]. 

In a molecular dynamic simulation147 of bulk atomic diffusion by a vacancy mechanism, two atoms may occasionally jump together as a pair. The temperature of the simulation is close to the melting point of the crystal. In FTM studies of single atom and atomic cluster diffusion, the temperature is only about one tenth the melting point of the substrate. All cluster diffusion, except that in the (1 x 1) to (1 x 2) surface reconstruction of Pt and Ir (110) surfaces already discussed in Section 4.1.2(b), are consistent with mechanisms based on jumps of individual atoms.148,149 In fact, jumps of individual atoms in the coupled motion of adatoms in the adjacent channel of the W (112) surface can be directly seen in the FTM if the temperature of the tip is raised to near 270 K.150... 

F,G. Amar, A structural approach to the analysis of cluster dynamics, in The Chemical Physics of Atomic and Molecular Clusters, G. Scoles, Editor. 1990 Amsterdam, p. 99... 

In order to interpret the results of our experiments, optimal-control calculations were performed where a GA controlled 40 independent degrees of freedom in the laser pulses that were used in a molecular dynamics simulation of the laser-cluster interactions for Xejv clusters with sizes ranging from 108 to 5056 atoms/cluster. These calculations, which are reported in detail elsewhere [67], showed optimization of the laser-cluster interactions by a sequence of as many as three laser pulses. Detailed inspection of the simulations revealed that the first pulse in this sequence initiates the cluster ionization and starts the expansion of the cluster, while the second and third pulse optimize two mechanisms that are directly related to the behaviour of the electrons in the cluster. We consistently observe that the second pulse in the three-pulse sequence arrives a time delay where the conditions for enhanced ionization are met. In other words, the second pulse arrives at a time where the ionization of atoms is assisted by the proximity of surrounding ions. The third peak is consistently observed at a delay where the collective oscillation of the quasi-free electrons in the cluster is 7t/2 out of phase with respect to the driving laser field. For a driven and damped oscillator this phase-delay represents an optimum for the energy transfer from the driving force to the oscillator. 

This method of preparation of supported metal catalyst requires a closed reactor to perform the preparation in the absence of water, so both the organic solvent and the oxide support must be carefully dehydrated. The method is based on the following principle the metal is evaporated and co-condensed with the organic to 77 K on the walls of the reactor. Under dynamic vacuum, the co-condensate is then warmed up to 195 K, and melted. The oxide support is impregnated with the solvated metal atom (cluster) at the same temperature, After a given time of contact, the slurry is warmed up to ambient temperature, and the solvent is eliminated, after which the sample can be dried. 

R. S. Berry, Atomic Clusters Powerful Tools to Probe Complex Dynamics, Adv. Chem. Phys. Part B 130, 3 (2005). 

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