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  • 1
    Digitale Medien
    Digitale Medien
    Ab initio configuration interaction study of excited states of LiNa3 and Li2Na2 clusters: Interpretation of absorption spectra (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4934-4944 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The ab initio configuration-interaction (CI) study of excited states of mixed alkali metal tetramers LiNa3 and Li2Na2 accounts for spectroscopic patterns obtained from the depletion spectra of neutral species, reproduces observed excitation energies and intensities for allowed transitions, and permits an assignment of cluster structures. For both mixed tetramers, the rhombic forms with a Li atom or atoms on the short diagonal are the most stable structures and give rise to predicted spectra in full agreement with the measured ones. The exact location of Li atoms seems to be more important in Li2Na2 than in LiNa3 since in the former case, only one isomer reproduces all features of the recorded spectrum.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462736
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  • 2
    Digitale Medien
    Digitale Medien
    Effective core potential-configuration interaction study of electronic structure and geometry of small neutral and cationic Agn clusters: Predictions and interpretation of measured properties (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7981-7994 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The ground state geometries of small neutral Agn(n=2–9) and cationic Agn+ (n=2–9) clusters have been determined in the framework of the Hartree–Fock and complete active space self-consistent field (CASSCF) procedure employing a relativistic effective core potential (RECP) accounting for core–valence correlation effects (CVC). Similarities and differences between topologies of neutral and charged structures have been found. Large scale configuration interaction (CI) calculations for 5s electrons only have been carried out for determining stabilities and ionization potentials (IP). A comparison between predicted and measured observables allows tentative geometrical assignments. Structural and electronic properties of small Ia and Ib clusters are compared.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464552
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  • 3
    Digitale Medien
    Digitale Medien
    Evolution of the electronic structure of lithium clusters between four and eight atoms (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1793-1809 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Absorption spectra of lithium clusters containing four to eight atoms have been measured using depletion spectroscopy. Few intense transitions are observed, always located in two predominant spectral regions, ∼480 and 680 nm. The spectra are interpreted using ab initio configuration interaction (CI) calculations, leading to a complete characterization of the excited states and a straightforward determination of the ground state geometrical structure. Intense transitions are explained by interference effects in the transition amplitude and symmetry considerations. Comparisons with semiclassical models, in which an effective mass correction is introduced, are also presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462846
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  • 4
    Digitale Medien
    Digitale Medien
    Approximate calculations of correlation energy using one-electron density-functional procedures: Application to Lin and Nan clusters (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6645-6654 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Nonlocal-density-functional (NLDF) procedures using restricted Hartree–Fock (HF) electron density have been adopted to determine the geometries and stabilities of neutral and cationic Lin and Nan (n=1–9) clusters and their ionization potentials. The NLDF yields parallel results to those previously obtained from all-electron configuration-interaction (CI) procedures, and as expected it accounts for the contributions of the correlation energy which are not present in truncated CI. In addition, a comparison between the results obtained from the local-density functional (LDF) without and with self-interaction correction has been carried out. The LDF procedure yields results for cluster stabilities which differ up to 10%–15% from those obtained from the NLDF schemes. This shows clearly that the results obtained from LDF and NLDF schemes are substantially different for calculated properties involving mainly correlation energy differences, provided that an exact HF exchange potential is used.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458302
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  • 5
    Digitale Medien
    Digitale Medien
    Quantum molecular interpretation of the absorption spectra of Na5, Na6, and Na7 clusters (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7938-7958 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462346
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  • 6
    Digitale Medien
    Digitale Medien
    An ab initio configuration interaction study of the reaction between small lithium clusters (Li4, Li6) and H2 molecule (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5533-5543 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A reaction path for the Li4+H2 interaction has been determined allowing for the relaxation and the reconstruction of the system. For various steps along the reaction path characterized by the given values of one or two geometrical parameters the full geometry optimization of the remaining variables has been carried out in the framework of the Hartree–Fock (HF) procedure. The configuration interaction (CI) energies for the optimal HF geometries in each step have been calculated using multireference diexcited (MRD-CI) procedure. The calculated dissociation energy for the molecular hydrogen is reduced from 103.6 to 19.6 kcal/mol in the presence of Li tetrameter. During the first stage of the reaction path referred as "dissociative chemisorption'' the geometry of the Li tetrameter does not change substantially. After dissociation of H2 the full reconstruction of the tetrameter takes place leading to a local minimum which is separated from the lowest minimum by a moderate barrier along the chosen reaction path. The stable compound has the form of deformed rhombus with two hydrogen atoms bridging two neighboring rhombus sides. The preliminary calculations using complete active space self-consistent field procedure followed by direct CI carried out for the Li6+H2 interaction in the C2v symmetry yield fairly stable three dimensional LI6H2 compound, which can be formed after passing an energy barrier of comparable size at the present level of calculation as that found for the Li4+H2 reaction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.460489
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  • 7
    Digitale Medien
    Digitale Medien
    Compact formulation of multiconfigurational response theory. Applications to small alkali metal clusters (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3121-3140 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A new Green's functions oriented formulation of multiconfigurational response theory is presented. The consistent use of Fourier integrals simplifies the formalism considerably with respect to previous derivations and leads to compact expressions for (exact and) approximate response functions of arbitrary orders. Applications of multiconfigurational linear response (MCLR) theory to the interpretation of depletion spectra of Li4, Na4, and Na6 clusters are shown. The results are compared to those obtained from large-scale configuration interaction calculations, illustrating that MCLR yields an adequate description of optically allowed transitions and oscillator strengths provided an appropriate active space has been chosen.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464086
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  • 8
    Digitale Medien
    Digitale Medien
    Ab initio predictions of structural and optical response properties of Na+n clusters: Interpretation of depletion spectra at low temperature (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1427-1440 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.470909
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  • 9
    Digitale Medien
    Digitale Medien
    Effective core potential-configuration interaction study of electronic structure and geometry of small anionic Agn clusters: Predictions and interpretation of photodetachment spectra (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 490-506 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.466964
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  • 10
    Digitale Medien
    Digitale Medien
    Electronic properties and geometric structures of Li4H and Li9H from optical absorption spectra (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 2727-2736 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.468649
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