Classical ion trajectory simulations

To our knowledge, this is the first study of the relaxations of an oxide surface by GIXS, and the first experimental determination of the relaxation and termination of the a-Al203(0001) surface. Another determination has been performed very recently by combining time-of-flight scattering and recoiling spectrometry with LEED and classical ion trajectory simulations [59], with essentially the same results. 

Classical Ion Trajectory Simulations. Classical ion trajectory simulations were carried out by means of the three-dimensional scattering and recoiling imaging code (SARIC) developed in this laboratory. SARIC is based on the binary collision approximation, uses the ZBL universal potential to describe the interactions between atoms, and includes both out-of-plane and multiple scattering. Details of the simulation have been published elsewhere 11). 

Aqueous processing, precursors for ferroelectric thin films, 95-104 Autocompensated surface structure of GaN film on sapphire experimental description, 26-27 experimental procedure classical ion trajectory simulations, 28 GaN sample, 27 first-layer species... 

Classical ion trajectory computer simulations based on the BCA are a series of evaluations of two-body collisions. The parameters involved in each collision are tire type of atoms of the projectile and the target atom, the kinetic energy of the projectile and the impact parameter. The general procedure for implementation of such computer simulations is as follows. All of the parameters involved in tlie calculation are defined the surface structure in tenns of the types of the constituent atoms, their positions in the surface and their themial vibration amplitude the projectile in tenns of the type of ion to be used, the incident beam direction and the initial kinetic energy the detector in tenns of the position, size and detection efficiency the type of potential fiinctions for possible collision pairs. 

In conclusion, these gas-phase measurements provide new elues to the role of solvation in ion-moleeule reaetions. For the first time, it is possible to study intrinsie reactivities and the extent to which the properties of gas-phase ion-moleeule reaetions relate to those of the eorresponding reactions in solution. It is clear, however, that gas-phase solvated-ion/moleeule reaetions in which solvent moleeules are transferred into the intermediate elusters by the nucleophile cannot be exaet duplieates of solvated-ion/ molecule reactions in solution in which solvated reactants exchange solvent molecules with the surrounding bulk solvent [743]. For a selection of more recent experimental [772] and theoretical studies of Sn2 reactions in gas phase and solution by classical trajectory simulations [773], molecular dynamics simulations [774, 775], ab initio molecular orbital calculations [776, 777], and density functional theory calculations [778, 779], see the references given. For studies of reactions other than Sn2 ion-molecule processes in the gas phase and in solution, see reviews [780, 781]. 

The classical trajectory simulations were carried out with VENUS interfaced with the semiempirical electronic structure theory computer program MOPAC. To simulate experimental conditions for (gly-H) -I-diamond collisions, the center of a beam of (gly-H)+ ion projectiles is aimed at the center of the surface, with fixed incident angle 0, and fixed initial translational energy, E,. The radius of the beam was chosen so that the beam overlapped a unit area on the surface. For each trajectory, the projectile was randomly placed in the cross section of this beam and then randomly rotated about its center of mass so that it had an initial random orientation with respect to the surface. The azimuthal angle, %, between the beam and a fixed plane perpendicular to the surface, was sampled randomly between 0 and 2n. Such a random sampling of X simulates collisions with different domains of growth on the diamond surface. 

Once the initial and boundary conditions are specified, the classical equations of motion are integrated as in any other simulation. From the start of the trajectory, the atoms are free to move under the influence of the potential. One simply identifies reaction mechanisms and products during the dynamics. For the case of sputtering, the atomic motion is integrated until it is no longer possible for atoms and molecules to eject. The final state of ejected material above the surface is then evaluated. Properties of interest include the total yield per ion, energy and angular distributions, and the structure and... 

The first example of the application of atomistic simulation to a materi-als-related area is probably the work of Vineyard and co-workers. They used classical trajectories to model damage induced in a solid by bombardment with ions having hyperthermal kinetic energies. These calculations, which were done at about the same time as Rahman s initial studies on liquids, provided important data related to damage depth as well as new insights into many-body collisions in solids. The potentials used were continuous pair-additive interactions similar to those employed in Rahman s simulations. 

Before discussing applications of the SE-SCM (and variants thereof) to the description of cluster fission, we note that for atomic and molecular clusters microscopic descriptions of energetics and dynamics of fission processes, based on modern electronic structure calculations in conjunction with molecular dynamics simulations (where the classical trajectories of the ions, moving on the concurrently calculated Born-Oppenheimer (BO) electronic potential-energy surface, are obtained via integration of the Newtonian... 

The interaction potential used in these simulations derives from the polarizable ion model [15]. It can be described as the sum of four different contributions charge-charge, dispersion, overlapped repulsion, and polarization, as previously described by Salanne et al. [16].This code is dedicated to calculations in ionic liquids. Via classical MD calculations, it allows generating the trajectories of ions inside a periodically replicated simulation cell, and then extracting the relevant physico-chemical properties of the melt. 

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