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  • 1
    ISSN: 1432-0649
    Keywords: PACS: 31.15Ar; 31.15Qg; 31.50+w
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Stationary spectra offer information on the interplay between the structures and the nature of electronic excitations reflecting bonding properties, as shown by comparing Sin with Agn (n=4-6) clusters. In order to study the dynamical properties, simulations and analysis of femtosecond (fs) time-resolved pump–probe or pump–dump signals have been carried out, which allows us to determine the timescales and the nature of configurational changes versus internal vibrational relaxation (IVR) in electronic ground or excited states. For this purpose we have developed a multi-state ab initio molecular dynamics (involving ground as well as adiabatic or non-adiabatic excited electronic states) on the timescale of the nuclear motion, using the time evolution of a thermal ensemble in the Wigner representation. The combination of ab initio quantum-chemical methods used for the molecular dynamics ‘on the fly’ and the Wigner-distribution approach for the description of the motion of the nuclei also allowed the accurate determination of pump–probe and pump–dump signals under temperature-dependent initial conditions. We use this novel combination of methods to investigate the dynamics in excited states of non-stoichiometric NanFn-1 clusters with a single excess electron. The timescales of the structural relaxation in excited states versus intramolecular vibrational relaxation processes have been determined, as illustrated for the example of Na4F3. This is the first study of the system with 15 degrees of freedom for which the dynamics in the excited states has been carried out without the precalculation of the energy surfaces.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 2727-2736 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Optical absorption spectra of Li4H and Li9H clusters have been recorded by depletion spectroscopy in the visible range. From comparison with ab initio calculations, geometries of both clusters are identified. The hydrogen atom assumes a peripheral position bridging two and three Li atoms in the planar and three-dimensional structures of Li4H and Li9H, respectively. Na4F and Na9F clusters are also theoretically studied and it is shown how the strong electronegativity of the F atom leads to different geometries than in lithium hydrids. Finally, the metallic character of these clusters is discussed and in both cases, the hydrogen or fluorine atom localizes one valence electron. However, the optical absorption spectra are much broader than in pure Lin and Nan clusters due to the lower symmetry. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground state geometries of small anionic Ag−n(n=2–9) clusters were determined in the framework of the Hartree–Fock procedure employing a relativistic effective core potential (RECP) accounting for core–valence correlation (CVC) effects. Large scale configuration interaction (CI) calculations for 5s electrons only were carried out in order to determine the ground state energies of anionic and neutral species as well as of excited states of the latter in the geometries of the former. The calculated vertical detachment and excitation energies account for the observed photodetachment spectroscopic patterns and permit an assignment of the cluster geometries. Structural and electronic properties of small Ia and Ib anionic clusters are compared.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1427-1440 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We show that a comparison of the depletion spectra of Na+n (n=2–9,11,21) clusters recorded at low temperature and optically allowed transitions determined for the stable structures using ab initio methods accounting for electron correlation allows the assignment of the cluster geometry to the measured features. Due to the large mobility of atoms in alkali metal clusters, the influence of temperature on structural and electronic properties is significant. The lowering of temperature reveals new spectroscopic features which are structure dependent. Optical response properties of small cationic Na+n clusters are characterized by rich molecularlike spectroscopic patterns, also with increasing size, and differ substantially from those found for neutral clusters. It has been clearly demonstrated that not only the number of valence electrons but its mutual interplay with the geometric properties determine optical response features. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7938-7958 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The configuration-interaction study of the excited states of the most-stable structures of Na5, Na6, and Na7 clusters employing ab initio effective-core potential corrected by the core polarization potential predicts spectroscopic patterns which are in good agreement with the measured depletion spectra. A comparison of the transition energies and the oscillator strengths with the experimental data makes possible tentative structural assignments. Planar Na5 and Na6 structures and the three-dimensional pentagonal bipyramid for Na7 appear responsible for the recorded spectra. The full agreement between theory and experiment is present for Na6 and Na7. The measured cross sections and calculated oscillator strengths for Na5 compare better for lower transition energies than for higher ones. A many-electron description of the excited states of Na5, Na6, and Na7 yields a complete quantum molecular interpretation of the absorption spectra. From a comparison of the experimental and theoretical results the conclusion has been drawn that a transition from planarity to the three dimensionality takes place for Na7.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0301-0104
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1572-9486
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The aim of this contribution is to show that quantum chemistry has suitable tools to extract the specific properties of small metallic and mixed non-stoichiometric clusters which cannot be obtained by extrapolation from the bulk properties to the atom. For this purpose, first the main features of the methods used for the calculations of the ground and excited states of clusters valid at zero temperature (T = 0) will be sketched and the factors determining accuracy of results will be pointed out. The structural and optical response properties of cationic clusters as a function of size will be presented and compared with experimental data. The series of non-stoichiometric alkali-halide clusters containing single and multiple excess electrons will serve as prototypes to study a possible “metal-insulator transition” and “segregation into metallic and ionic parts” in finite systems. Second, an outline of ab initio molecular dynamics methods based on gradient corrected density functional approach with gaussian basis used for determination of temperature dependent ground state properties will be presented. Different temperature behavior of distinct type of structures will be illustrated on an example of cluster.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 26 (1993), S. 17-22 
    ISSN: 1434-6079
    Keywords: 31.20.Tz ; 31.50.+w ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The contribution of quantum chemicalab — initio studies of optical response in small metal clusters towards understanding of their specific electronic and structural properties has been presented. The role of cluster size, geometry, number of valence electrons and chemical composition has been pointed out. It has been shown that an appropriate many-electron description of excited states for stable cluster structures allows for the quantum molecular interpretation of the absorption spectra and other optical probles. The nature of excitations responsible for characteristic spectroscopic patterns has been discussed.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 9 (1999), S. 183-187 
    ISSN: 1434-6079
    Keywords: PACS: 31.15.Ar Ab initio calculations – 31.15.Dv Coupled cluster theory – 31.50.+w Excited states – 36.40.Mr Spectroscopy and geometrical structure of clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We present calculations of absorption patterns in large energy intervals for the stable structures of oxygen-doped- and pure-silver clusters using the linear-response-type approach which allows one to correlate all 11 and 6 electrons per Ag and O atoms, respectively. For this purpose, we designed a new 11-electron relativistic effective core potential (11e–RECP) for Ag atoms at the correlated level of theory, which, together with the associated AO basis set, provide an accurate description of excited states. This has been evidenced by the comparison of our results with available experimental data. We found that inclusion of d electrons in the RECP, as well as in the correlation treatment, is important for an accurate prediction of the complete absorption spectra. Moreover, the influence of d electrons of Ag atoms becomes pronounced, even for structural properties of AgnO clusters. Also, the electrons of oxygen are strongly involved in excitations besides those of Ag-valence electrons, leading to intense transitions spread in a large energy interval. The role O plays in Ag n O clusters differs substantially from the one it plays in oxygen-doped alkali clusters, because of the participation of the d electrons of Ag atoms.
    Type of Medium: Electronic Resource
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