Atomic and electronic structures of the electronically magic Na 59 + cluster are investigated using density functional theory and an ab initio pseudopotential. Two atomically closed-shell structures are found, but none of these "double-magic" structures is the global ground state at T = 0. Simulated annealing with ab initio molecular dynamics yields a more stable amorphous, but "spherical" atomic structure that closely resembles structures obtained from a simple classical model of 59 point charges in a spherical harmonic well. This indicates that the sodium ions arrange into a structure that is dictated by a stiff spherical background of the closed 58-electron configuration. Upon heating, this cluster melts already at about 175 K displaying a minute latent heat of 2.3 meV/ atom. The simulated photoelectron spectrum at 260 K reproduces the 1g, 2p, and 1f peaks observed previously in the experiment.
The finite-temperature dynamics of WAu12, incorporating both electronic and structural effects, is studied using a density-functional-based Born-Oppenheimer molecular dynamics method. Molecular dynamics simulations for monomolecular WAu12 suggest a surface-melting-type behaviour of the angular degrees of freedom between 366 and 512 K. Thermally averaged electron density-of-states of WAu12 are compared to the experimental photoelectron spectra of WAu12(-).
The lowest energy configurations of close-packed clusters up to N = 110 atoms with stacking faults are studied using the Monte Carlo method with a Metropolis algorithm. Two types of contact interactions, a pair-potential and a many-atom interaction, are used. Enhanced stability is shown for N = 12, 26, 38, 50, 59, 61, 68, 75, 79, 86, 100 and 102, of which only the sizes 38, 75, 79, 86, and 102 are pure FCC clusters, the others having stacking faults. A connection between the model potential and density functional calculations is studied in the case of Al100. The density functional calculations are consistent with the experimental fact that there exist epitaxially grown FCC clusters starting from relatively small cluster sizes. Calculations also show that several other close-packed motifs exist with comparable total energies.
Because of the different physiological impact that stereoisomers may have, it is often vital to separate these forms from one another. Because of their structural similarity, the separation is usually difficult to achieve and zones may elute very close to each other. This is a particular problem in capillary electrophoresis, where the repeatability of absolute migration times is fairly poor, mainly due to the irreproducibility of the electroosmotic flow. The separation is usually repeatable, however, and when the disturbing effects are eliminated by using a migration index system incorporating two marker compounds the identification of the enantiomers becomes extremely good. Relative standard deviation (RSD) values less than 0.1% for the migration index of each enantiomer were obtained in both intra-day and day-to-day (6 days) studies. The best separation was achieved with the electrolyte solution made of 40 mM borate, 32 mM sodium dodecyl sulfate (SDS), 12 mM beta-cyclodextrin (beta-CD), and 6 mM alpha-cyclodextrin (alpha-CD) at pH 9.3.
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