Photoelectron spectra of aluminum cluster anions: Temperature effects and ab initio simulations

Photoelectron (PES) spectra from aluminum cluster anions (from 12 to 15 atoms) at various temperature regimes, were studied using ab-initio molecular dynamics simulations and experimentally. The calculated PES spectra, obtained via shifting of the simulated electronic densities of states by the self-consistently determined values of the asymptotic exchange-correlation potential, agree well with the measured ones, allowing reliable structural assignments and theoretical estimation of the clusters' temperatures.Comment: RevTex, 3 gif figures. Scheduled for Oct 15, 1999, issue of Phys. Rev. B as Rapid Communicatio

Structure and Magnetism of Neutral and Anionic Palladium Clusters

The properties of neutral and anionic Pd_N clusters were investigated with spin-density-functional calculations. The ground state structures are three-dimensional for N>3 and they are magnetic with a spin-triplet for 2<=N<=7 and a spin nonet for N=13 neutral clusters. Structural- and spin-isomers were determined and an anomalous increase of the magnetic moment with temperature is predicted for a Pd_7 ensemble. Vertical electron detachment and ionization energies were calculated and the former agree well with measured values for anionic Pd_N clusters.Comment: 5 pages, 3 figures, fig. 2 in color, accepted to Phys. Rev. Lett. (2001

Optical response of small silver clusters

The time-dependent local density approximation is applied to the optical response of the silver clusters, Ag_2, Ag_3, Ag_8 and Ag_9^+. The calculation includes all the electrons beyond the closed-shell Ag^{+11} ionic core, thus including for the first time explicitly the filled d-shell in the response. The excitation energy of the strong surface plasmon near 4 eV agrees well with experiment. The theoretical transition strength is quenched by a factor of 4 with respect to the pure s-electron sum rule in Ag_8 due to the d-electrons. A comparable amount of strength lies in complex states below 6 eV excitation. The total below 6 eV, about 50% of the s sum rule, is consistent with published experiments.Comment: 13 pages RevTex and 9 Postscript figure

Continuous symmetry of C60 fullerene and its derivatives

Conventionally, the Ih symmetry of fullerene C60 is accepted which is supported by numerous calculations. However, this conclusion results from the consideration of the molecule electron system, of its odd electrons in particular, in a close-shell approximation without taking the electron spin into account. Passing to the open-shell approximation has lead to both the energy and the symmetry lowering up to Ci. Seemingly contradicting to a high-symmetry pattern of experimental recording, particularly concerning the molecule electronic spectra, the finding is considered in the current paper from the continuous symmetry viewpoint. Exploiting both continuous symmetry measure and continuous symmetry content, was shown that formal Ci symmetry of the molecule is by 99.99% Ih. A similar continuous symmetry analysis of the fullerene monoderivatives gives a reasonable explanation of a large variety of their optical spectra patterns within the framework of the same C1 formal symmetry exhibiting a strong stability of the C60 skeleton.Comment: 11 pages. 5 figures. 6 table

Allogamy-Autogamy Switch Enhance Assortative Mating in the Allotetraploid Centaurea seridis L. Coexisting with the Diploid Centaurea aspera L. and Triggers the Asymmetrical Formation of Triploid Hybrids

[EN] Hybridization between tetraploids and its related diploids is generally unsuccessful in Centaurea, hence natural formation of triploid hybrids is rare. In contrast, the diploid Centaurea aspera and the allotetraploid C. seridis coexist in several contact zones where a high frequency of triploid hybrids is found. We analyzed the floral biology of the three taxa to identify reproductive isolation mechanisms that allow their coexistence. Flowering phenology was recorded, and controlled pollinations within and between the three taxa were performed in the field. Ploidy level and germination of progeny were also assessed. There was a 50% flowering overlap which indicated a phenological shift. Diploids were strictly allogamous and did not display mentor effects, while tetraploids were found to be highly autogamous. This breakdown of self-incompatibility by polyploids is first described in Centaurea. The asymmetrical formation of the hybrid was also found: all the triploid intact cypselae came from the diploid mothers pollinated by the pollen of tetraploids. Pollen and eggs from triploids were totally sterile, acting as a strong triploid block. These prezygotic isolation mechanisms ensured higher assortative mating in tetraploids than in diploids, improving its persistence in the contact zones. However these mechanisms can also be the cause of the low genetic diversity and high genetic structure observed in C. seridis.Ferriol Molina, M.; Garmendia, A.; Ana Gonzalez; Merle Farinós, HB. (2015). Allogamy-Autogamy Switch Enhance Assortative Mating in the Allotetraploid Centaurea seridis L. Coexisting with the Diploid Centaurea aspera L. and Triggers the Asymmetrical Formation of Triploid Hybrids. PLoS ONE. 10(10):1-13. doi:10.1371/journal.pone.0140465S1131010Jiao, Y., Wickett, N. J., Ayyampalayam, S., Chanderbali, A. S., Landherr, L., Ralph, P. E., … dePamphilis, C. W. (2011). Ancestral polyploidy in seed plants and angiosperms. Nature, 473(7345), 97-100. doi:10.1038/nature09916Wood, T. E., Takebayashi, N., Barker, M. S., Mayrose, I., Greenspoon, P. B., & Rieseberg, L. H. (2009). The frequency of polyploid speciation in vascular plants. Proceedings of the National Academy of Sciences, 106(33), 13875-13879. doi:10.1073/pnas.0811575106ROMASCHENKO, K., ERTUǦRUL, K., SUSANNA, A., GARCIA-JACAS, N., UYSAL, T., & ARSLAN, E. (2004). New chromosome counts in the Centaurea Jacea group (Asteraceae, Cardueae) and some related taxa. Botanical Journal of the Linnean Society, 145(3), 345-352. doi:10.1111/j.1095-8339.2004.00292.xHardy, O. J., de Loose, M., Vekemans, X., & Meerts, P. (2001). Allozyme segregation and inter-cytotype reproductive barriers in the polyploid complex Centaurea jacea. Heredity, 87(2), 136-145. doi:10.1046/j.1365-2540.2001.00862.xKOUTECKÝ, P., BAĎUROVÁ, T., ŠTECH, M., KOŠNAR, J., & KARÁSEK, J. (2011). Hybridization between diploidCentaurea pseudophrygiaand tetraploidC. jacea(Asteraceae): the role of mixed pollination, unreduced gametes, and mentor effects. Biological Journal of the Linnean Society, 104(1), 93-106. doi:10.1111/j.1095-8312.2011.01707.xKoutecký, P. (2012). A diploid drop in the tetraploid ocean: hybridization and long-term survival of a singular population of Centaurea weldeniana Rchb. (Asteraceae), a taxon new to Austria. Plant Systematics and Evolution, 298(7), 1349-1360. doi:10.1007/s00606-012-0641-5Mráz, P., Španiel, S., Keller, A., Bowmann, G., Farkas, A., Šingliarová, B., … Müller-Schärer, H. (2012). Anthropogenic disturbance as a driver of microspatial and microhabitat segregation of cytotypes of Centaurea stoebe and cytotype interactions in secondary contact zones. Annals of Botany, 110(3), 615-627. doi:10.1093/aob/mcs120Olšavská, K., & Löser, C. J. (2013). Mating System and Hybridization of the Cyanus triumfetti and C. montanus Groups (Asteraceae). Folia Geobotanica, 48(4), 537-554. doi:10.1007/s12224-013-9155-3Španiel, S., Marhold, K., Hodálová, I., & Lihová, J. (2008). Diploid and Tetraploid Cytotypes of Centaurea stoebe (Asteraceae) in Central Europe: Morphological Differentiation and Cytotype Distribution Patterns. Folia Geobotanica, 43(2), 131-158. doi:10.1007/s12224-008-9008-7HARDY, O. J., VANDERHOEVEN, S., DE LOOSE, M., & MEERTS, P. (2000). Ecological, morphological and allozymic differentiation between diploid and tetraploid knapweeds (Centaurea jacea) from a contact zone in the Belgian Ardennes. New Phytologist, 146(2), 281-290. doi:10.1046/j.1469-8137.2000.00631.xFerriol, M., Garmendia, A., Ruiz, J. J., Merle, H., & Boira, H. (2012). Morphological and molecular analysis of natural hybrids between the diploidCentaurea asperaL. and the tetraploidC. seridisL. (Compositae). 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T., Palsson, S., Sigurgeirsson, A., & Anamthawat-Jonsson, K. (2007). Morphological Variation among Betula nana (diploid), B. pubescens (tetraploid) and their Triploid Hybrids in Iceland. Annals of Botany, 99(6), 1183-1193. doi:10.1093/aob/mcm060Husband And, B. C., & Schemske, D. W. (2000). Ecological mechanisms of reproductive isolation between diploid and tetraploidChamerion angustifolium. Journal of Ecology, 88(4), 689-701. doi:10.1046/j.1365-2745.2000.00481.xKruskal, W. H., & Wallis, W. A. (1952). Use of Ranks in One-Criterion Variance Analysis. Journal of the American Statistical Association, 47(260), 583-621. doi:10.1080/01621459.1952.10483441Dunn, O. J. (1961). Multiple Comparisons among Means. Journal of the American Statistical Association, 56(293), 52-64. doi:10.1080/01621459.1961.10482090HARVILLE, D. A. (1974). Bayesian inference for variance components using only error contrasts. Biometrika, 61(2), 383-385. doi:10.1093/biomet/61.2.383McCullagh, P., & Nelder, J. A. (1989). Generalized Linear Models. doi:10.1007/978-1-4899-3242-6Lambert, D. (1992). Zero-Inflated Poisson Regression, with an Application to Defects in Manufacturing. Technometrics, 34(1), 1. doi:10.2307/1269547Vuong, Q. H. (1989). Likelihood Ratio Tests for Model Selection and Non-Nested Hypotheses. Econometrica, 57(2), 307. doi:10.2307/1912557Ferriol, M., Llorens, L., Gil, L., & Boira, H. (2008). Influence of phenological barriers and habitat differentiation on the population genetic structure of the balearic endemic Rhamnus ludovici-salvatoris Chodat and R. alaternus L. Plant Systematics and Evolution, 277(1-2), 105-116. doi:10.1007/s00606-008-0110-3Colas, B., Olivieri, I., & Riba, M. (2001). Spatio-temporal variation of reproductive success and conservation of the narrow-endemic Centaurea corymbosa (Asteraceae). Biological Conservation, 99(3), 375-386. doi:10.1016/s0006-3207(00)00229-9Felber, F., & Bever, J. D. (1997). 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Orbital interactions and chemical reactivity of metal particles and metal surfaces

A review is presented with 101 refs. on chem. bonding to metal surfaces and small metal particles demonstrating the power of symmetry concepts to predict changes in chem. bonding. Ab-initio calcns. of chemisorption to small particles, as well as semiempirical extended Hueckel calcns. applied to the study of the reactivity of metal slabs are reviewed. On small metal particles, classical notions of electron promotion and hybridization are found to apply. The surroundings of a metal atom (ligands in complexes, other metal atoms at surfaces), affect bonding and reactivity through the prehybridization they induce. A factor specific for large particles and surfaces is the required localization of electrons on the atoms involved in the metal surface bond. At the surface, the bond energy is found to relate to the grou8p orbital local d. of states at the Fermi level. The use of this concept is extensively discussed and illustrated for chemisorption of CO and dissocn. of NO on metal surfaces. A discussion is given of the current decompn. schemes of bond energies and related concepts (exchange (Pauli)-repulsion, polarization, charge transfer). The role of non-orthogonality of fragment orbitals and of kinetic and potential energy for Pauli repulsion and (orbital) polarization is analyzed. Numerous examples are discussed to demonstrate the impact of those concepts on chem. bonding theor

Ab initio studies of structures and properties of small potassium clusters

We have studied the structure and properties of potassium clusters containing even number of atoms ranging from 2 to 20 at the ab initio level. The geometry optimization calculations are performed using all-electron density functional theory with gradient corrected exchange-correlation functional. Using these optimized geometries we investigate the evolution of binding energy, ionization potential, and static polarizability with the increasing size of the clusters. The polarizabilities are calculated by employing Moller-Plesset perturbation theory and time dependent density functional theory. The polarizabilities of dimer and tetramer are also calculated by employing large basis set coupled cluster theory with single and double excitations and perturbative triple excitations. The time dependent density functional theory calculations of polarizabilities are carried out with two different exchange-correlation potentials: (i) an asymptotically correct model potential and (ii) within the local density approximation. A systematic comparison with the other available theoretical and experimental data for various properties of small potassium clusters mentioned above has been performed. These comparisons reveal that both the binding energy and the ionization potential obtained with gradient corrected potential match quite well with the already published data. Similarly, the polarizabilities obtained with Moller-Plesset perturbation theory and with model potential are quite close to each other and also close to experimental data.Comment: 33 pages including 10 figure