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  • 1
    Electronic Resource
    Electronic Resource
    Green's function calculation of the valence photoemission spectra of PF3 and NiPF3 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 6953-6957 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed ab initio algebraic diagrammatic construction [ADC(3)] Green's function calculations of the valence photoemission spectra of PF3 and NiPF3. We obtained overall good agreement with experiment for both the free PF3 molecule and the PF3 molecule chemisorbed on a Ni(111) metal surface. A comparison to NiCO shows that there are certain similarities between NiPF3 and NiCO, not only in the σ donor–π acceptor bonding mechanism in the ground state, but also in the metal–ligand CT excitations associated with the creation of a valence hole in the ligand. However, it appears that the many-body effect, such as the configuration interactions in the final ionized state, seems to be weaker for NiPF3 than for NiCO, judging from the main line spectral intensity. The quasiparticle picture of the 4e level breaks down completely as in the case of the 1π level of NiCO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463649
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  • 2
    Electronic Resource
    Electronic Resource
    Electron affinities, shake-up affinities, and ionization energies of S4 isomers (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8301-8308 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nine isomers of S4 (D∞h,D2h,D4h,D3h,D2i,C2v, C2h,C3v,Cs) have been studied with large basis sets in Green function, CASSCF, and single and multi reference CI approaches. The C2v and D2h isomers are found to be nearly equally stable with the C2v isomer 1 kcal/mol below the D2h form and the C2h isomer about 10 kcal/mol higher in energy. All isomers have an appreciable electron affinity and some have several bound negative ion states. Besides normal electron affinities they have shake-up affinities, which may also be strongly positive. The lowest ionization energies of the isomers range from 7.5 to 9 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461257
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  • 3
    Electronic Resource
    Electronic Resource
    Study of the valence electronic structure of ethyne by electron momentum spectroscopy and Green's function methods (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3468-3478 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The complete valence shell electron separation energy spectra and momentum distributions are measured for ethyne by high resolution electron momentum spectroscopy at a total energy of 1500 eV. Many-body calculations of the separation energies and spectroscopic factors using Green's function methods are carried out and compared with the data. The measured momentum distributions are compared with self-consistent-field (SCF) orbital wave functions, the SCF wave functions including d functions in the basis sets. The agreement between the measured momentum distributions and the SCF orbital momentum distributions is excellent. The inner valence 2σg orbital is found to be split severely by final state correlation effects. The agreement between the measured and calculated spectroscopic factors and separation energies is in general very good, although the measured separation energy spectra contain significant strength up to 50 eV, this strength being mainly of 2σg origin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459768
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  • 4
    Electronic Resource
    Electronic Resource
    Valence ionization of HCl. An investigation of many-body effects (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4331-4341 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Many-body Green's-function calculations which employ large configurational expansions and which are accurate to third and fourth order of perturbation theory are reported for the valence ionic states of HCl. Large polarized basis sets including Rydberg functions s-, p-, and d-type symmetries have been used. Third-order calculations are sufficient in the outer valence region, but in the inner valence region where the complete breakdown of the one-particle picture of ionization is observed a fourth-order theory is necessary in conjunction with large basis sets. The synchrotron and x-ray excited spectra can be assigned nearly up to the double-ionization threshold in a very satisfactory way. No indication of strong outer valence satellite lines is found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457740
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  • 5
    Electronic Resource
    Electronic Resource
    Valence ionization and the electron affinities of the open and cyclic forms of Se3 and Te3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3582-3588 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Se3 and Te3 exist as the S3 molecule in an open C2v and a closed D3h form with different electronic configurations but nearly the same total energy. The ionization spectra of Se3 and Te3 are calculated in both the C2v and D3h forms by many-body Green's function methods. The D3h forms behave quite regularly, but very strong correlation effects are found in the C2v forms. If a theory accurate to third order is used, satellite lines appear at the ionization threshold. If higher order terms are included the satellite lines at the ionization threshold experience a slight change in energy, but a considerable reduction of intensity. Se3 has a positive electron affinity in both the C2v and D3h forms (2B1, 2A'2, states), and Te3 appears to have two positive electron affinities (2B1, 2A1 for the C2v form and 2A2 and 2E' for the D3h form).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456890
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  • 6
    Electronic Resource
    Electronic Resource
    Many-body calculation of the valence photoemission spectrum of PdN2 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2767-2771 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed ab initio two hole one particle (2h1p) CI and algebraic diagrammatic construction [ADC(3)] Green's function calculations of the valence photoemission spectrum of PdN2. The spectral features obtained by two different reliable methods are similar. However, they disagree with the experimental spectrum of N2/Pd(111) system. The 1π and 5σ ionization peaks are interpreted to be so well separated (1.6 eV) according to the experimental assignment, but the present theoretical result shows that despite a much weaker metal–ligand bonding, they are almost degenerate as in the case of the CO/Ni, CO/Pd, and N2/Ni systems. The basic spectral features and the relative positions of the 1π and 5σ levels do not change much with an increase of the metal–ligand bond length (weaker bonding strength). This shows that further detailed experimental study of the valence photoemission spectrum of the N2/Pd system is needed. The many-body effects such as the breakdown of the quasiparticle picture for the ionization is much stronger in NiN2 that in PdN2, despite the widely held assumption that weak coupling leads to increased many-body effects. It is shown that the change of the valence spectral features of the adsorbate depends on a subtle change of the electronic structure of the substrate metal atom rather than the metal–ligand bond strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463067
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  • 7
    Electronic Resource
    Electronic Resource
    Many-body calculation of the valence photoemission spectrum of Fe(CO)5 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 373-379 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The valence photoemission spectrum of Fe(CO)5 is calculated by the ADC(3) Green's function method. The overall agreement with the experiment is good. It is shown that the quasiparticle picture (QPP) for the outer and inner valence levels (except the 8a‘2 level) derived primarily from CO ligand orbitals breaks down completely due to the one-hole/two-hole–one-particle (1h/2h1p) charge transfer (CT) coupling in the bonded system. Compared to Ni(CO)4 the many-electron effect is much stronger in Fe(CO)5. In Cr(CO)6 and Fe(CO)5 the 3d shell is incompletely filled, but in contrast to Cr(CO)6 in Fe(CO)5 there is no significant contribution from the local metal excitations. It is shown that for the 8a(large-closed-square)2 level the 1h state is still more stable than the 2h1p states. Consequently the main line (with an intensity of 0.76) is interpreted as the 1h state where the screening charge resides on the bonding orbital which is more polarized toward the ligand than in the ground state. The satellites are dominated by 2h1p configurations where the bonding to antibonding shake-up excitations occur. For the other CO derived levels the strong mixing of 1h and 2h1p configurations leads to the breakdown of the QPP of the ionization and thus a distinction between main line and satellite line becomes meaningless. For most of the levels, the strong dynamical metal–ligand CT hole–particle excitations, where the creation of two holes in the same metal orbital is involved, lead to the breakdown of the QPP of the ionization. A similar strong many-electron effect is also found in Cr(CO)6. For most of the outer and inner valence levels of these molecules, the QPP of the ionization breaks down.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461438
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  • 8
    Electronic Resource
    Electronic Resource
    The CO+O2 reaction on metal surfaces. Simulation and mean-field theory: The influence of diffusion (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3685-3692 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A computer simulation for the heterogeneous catalyzed oxidation of CO is presented. The simulation includes adsorption, CO diffusion, reaction, and CO2 desorption. It is found that a first-order phase transition occurs at yCO=y2 (yCO is the mole fraction of CO in the gas phase). In the interval [ y2,1], the catalyst is almost completely covered with CO, i.e., the catalyst is poisoned. The value of y2 is a function of the adsorption/diffusion ration. For no CO diffusion, Ziff, Gulary, and Barshad [Phys. Rev. Lett. 24, 2553 (1986)] found y2=0.525. In this paper, for A/D=1/40, y2=0.650. In a mean-field ansatz with infinite diffusion rate, one obtains y2=0.666. With a linear stability analysis, the dependence of y2 on different initial coverage values can be explained. An initial coverage of oxygen does not influence the value of y2, but with increasing initial coverage of CO, the value of y2 decreases. It will be shown that oscillations are not possible in this simple reaction system. The adsorbed O atoms form large clusters that are found to be fractal in nature. The fractal dimension Df is equal to 1.88. A percolation transition at yCO=0.520 is observed, which corresponds to a critical oxygen coverage of aitch-thetaO,crit.=0.561. At this oxygen coverage, an infinite cluster percolates through the lattice. The value of aitch-thetaO,crit. is nearly independent of the A/D ratio. In correlated percolation simulations, it is found that aitch-thetaO,crit.=0.559, which is in good agreement with the value obtained from the reaction system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459691
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  • 9
    Electronic Resource
    Electronic Resource
    A Monte Carlo simulation of the CO oxidation on probabilistic fractals (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 3082-3091 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study a model of the CO oxidation on percolation clusters which represent the surface of our system in the Monte Carlo simulation. We observe two phase transitions where the surface is completely covered (poisoned) by one species (in our system CO or O). These phase transitions are described by their order and the values of the mole fraction yCO of CO in the gas phase at y1 (O poisoning) and at y2 (CO poisoning). The interval (y1,y2) represents the reactive regime. The influence of the occupation probability p for generating a spanning cluster on the underlying square lattice, of the diffusion of CO and of the lattice size on the value and the character of the kinetic phase transitions is studied. Increasing p leads to a shift of y2 to larger values of yCO for all ratios of adsorption to diffusion events but the value of y1 is increased to a larger value of yCO only if diffusion is not allowed. In the case of diffusion the value of y1 is maximally independent of p. A change in the character of the phase transition at y2 from first order on regular lattices to second order is observed on percolation clusters (p≥pC=0.592 75). Here pC is the percolation threshold on the square lattice. The character becomes again first order if diffusion is allowed or if p exceeds 0.97. The observed effects may be understood as a result of the different ramification of the percolation clusters which strongly depends on p. The cluster structures are characterized by pair correlation functions. The lattice size shows for p near unity no significant effect on the values of y1 and y2 but its influence increases with decreasing p. We will show that the fractal dimension of the surface is not a useful quantity for predicting the positions and the character of the phase transitions for the reaction system studied here.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465161
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  • 10
    Electronic Resource
    Electronic Resource
    Diffusion and reaction in multicomponent systems via cellular-automaton modeling: A+B2 (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2032-2037 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A cellular-automaton model for the diffusion on a lattice is introduced. The spatial and temporal correlations that appear in the model are compared with the results of the correlated random walk, which has been obtained by Monte Carlo simulations. Very good agreement was found between these completely different simulations for the spatial correlations. The temporal correlations are quite different because of the nonequivalent temporal evolution of the two models. This new cellular automaton model is used to describe a reaction-diffusion system that represents the catalytic oxidation of CO on a metal surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464236
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