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  • 1
    Electronic Resource
    Electronic Resource
    Light scattering by alkali halide melts: A computer simulation study (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 918-927 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model for the interaction-induced polarizability of halide ions in condensed phases has been developed from ab initio electronic structure calculations. This model is incorporated into computer simulations of molten LiF, LiCl, and NaCl and used to calculate correlation functions of the polarizability in order to simulate the light scattering spectra. The results for the line shapes, frequency dependent depolarization ratio, and absolute intensity compare extremely well with the available experimental data. The relative importance of the contributions to the interaction-induced spectra from changes in the ionic polarizability caused by short-range overlap, ionic field-induced distortion, and dipole–induced dipole interactions is assessed and their distinctive spectral characteristics identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459982
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  • 2
    Electronic Resource
    Electronic Resource
    The Raman spectra of alkali halide melts: A theoretical description (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1980-1990 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical description of the light scattering (Raman) spectra of molten salts is presented. Expressions are derived to relate the spectra of the fluctuating polarizability induced by the ion Coulomb field and by the dipole–induced dipole mechanism to the spectra of the mass and charge density fluctuations (i.e., the dynamical structure factors). The theory thereby connects the spectral features seen in light scattering to well known dynamical processes in the ionic melt, such as the charge density wave (plasmon) and the ionic diffusive motion. The validity of this description is confirmed by evaluating the theoretical expression, using dynamical structure factors calculated in computer simulations, and comparing it with spectra calculated directly from the simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460995
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  • 3
    Electronic Resource
    Electronic Resource
    Hydration and mobility of ions in solution (1983)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 87 (1983), S. 5071-5083 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j150643a008
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  • 4
    Electronic Resource
    Electronic Resource
    In-crystal polarizability of the oxide ion (O2-) (1985)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 89 (1985), S. 2581-2585 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100258a031
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  • 5
    Electronic Resource
    Electronic Resource
    Cluster Formation in Sodium-Doped Zeolite Y: Ab-Initio Simulation Study (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 6697-6714 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100017a062
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  • 6
    Electronic Resource
    Electronic Resource
    The nature of the "vibrational modes" of the network-forming liquid ZnCl2 (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9859-9869 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The atomic motions responsible for features seen in the spectra of network-forming liquids above the relaxational frequency domain are conventionally described as vibrational, with the nature of the vibrational modes described either as local vibrations of the tetrahedral units of the network or as extended, phonon-like vibrations, depending on the standpoint of the observer. The validity of these apparently conflicting pictures of the atomic motions is examined by an instantaneous normal mode (INM) analysis of the network-forming liquid ZnCl2. Projections of the INM eigenvectors onto the idealized modes provides a way of quantifying the relationship between the actual and idealized modes. It is shown that individual INMs do not remotely conform to the modes envisaged in the simple pictures. Nevertheless, at the more coarse-grained level of identifying contributions to the density of states, the simple pictures do provide a qualitative guide to the character of the features which are observed. These findings apply to the modes calculated with several different models of the interactions, and appear to be fairly general. A detailed examination of the nature of the INMs which appear in the frequency domain of the boson peak observed in ZnCl2 is carried out and it is shown that these modes have a mixed acoustic wave and local torsional character. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477655
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  • 7
    Electronic Resource
    Electronic Resource
    On the observation of propagating sound modes at high momentum transfer in viscous liquids and glasses (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9027-9038 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamic structure factors, S(Q,ω), at a range of scattering vectors (Q) in the range 0.2〈Q〈3.0 Å−1 are calculated in a molecular dynamics (MD) simulation of the viscous, network-forming liquid, ZnCl2. At intermediate Q (0.2〈Q〈0.5 Å−1), Brillouin features, with shifts and widths proportional to Q and Q2, respectively, are observed. These features persist above the frequency of the "boson peak," in apparent discord with some suggestions for its origin. At high values of Q, close to the first peak of the static structure factor, a Q-dependent feature is seen in the inelastic part of S(Q,ω). This is analogous to a recent experimental observation on the similar, network-forming system B2O3 which was assigned to a "sound mode" contribution. An instantaneous normal mode (INM) analysis was applied to understand the relationship between these observations and the nature of the underlying modes of the liquid. The INM analysis accurately reproduces the observed (in MD) behavior of S(Q,ω) but does not support the existence of well-defined, plane-wave-like sound modes in the fluid in the relevant régimes of Q and ω. Alternative explanations of the origin of the Brillouin and S(Q)-dependent features are proposed on the basis of the INM results, and results related to the origin of the boson peak in the density of states are presented. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476349
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  • 8
    Electronic Resource
    Electronic Resource
    Instantaneous normal mode prediction for cation and anion diffusion in ionic melts (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 8616-8619 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Instantaneous normal mode (INM) analysis was undertaken for several ionic melts: NaCl at six distinct thermodynamic states, and for a particular state of liquid LiCl, LiF, KF, KI, NaI, ZnCl2, and CuCl. In this Communication, we show that, in most cases, the ratio between the diffusion constants for cations (Dca) and anions (Dan) is predicted from the average frequency of the real ("stable" 〈ωs〉) and imaginary ("unstable" 〈ωu〉) frequency modes of the projection of the total density of states on cations and anions, respectively. The proposed relationship, Dca/Dan=(mca〈sup ARRANGE="STAGGER"〉−1〈ωu〉ca〈ωs〉ca〈sup ARRANGE="STAGGER"〉−2)⋅(man〈sup ARRANGE="STAGGER"〉−1〈ωu〉an〈ωs〉an〈sup ARRANGE="STAGGER"〉−2)−1, where mi is the mass of a particular species, is suggested by Keyes' INM theory for diffusion [J. Chem. Phys. 101, 5081 (1994)], with the further assumption that the parameters which are related to the topology of the multidimensional potential surface are equal for cations and anions. The above equation is shown to be valid for the simple melts NaCl, LiCl, LiF, KF, KI, and NaI, but to fail for the network forming melt ZnCl2 and for CuCl, which shows fast ionic diffusion characteristics. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473917
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  • 9
    Electronic Resource
    Electronic Resource
    Raman scattering in the network liquid ZnCl2 relationship to the vibrational density of states (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4803-4811 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The light scattering (Raman) spectrum of ZnCl2 has been calculated in a computer simulation directly from molecular dynamics and by using an instantaneous normal modes (INM) approach. Good agreement between the spectra is reported. The calculations use a realistic model for the fluctuating polarizability of ZnCl2, derived from earlier work on simpler ionic melts. This contains several mechanisms which couple the radiation field to the ionic motion—short-range, dipole-induced dipole and hyperpolarization. INM analysis of ZnCl2 has previously shown how the character of the underlying vibrational modes changes across the density of states. Here it is shown that the efficiency of the coupling of a given mode to the radiation field depends strongly on its character and on the polarizability mechanism, so that the Raman spectra predicted for the different mechanisms differ markedly. A consequence is that the discrete Raman bands observed at high frequency in the polarized spectrum do not coincide with the spectrum of the localized, quasi-molecular ZnCl4 units of the network. Furthermore, the "light-vibration" coupling, relating the reduced Raman spectrum to the underlying vibrational density of states, is appreciably frequency dependent and different for each mechanism. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478368
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  • 10
    Electronic Resource
    Electronic Resource
    Unstable modes in ionic melts (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3256-3263 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Imaginary frequency instantaneous normal modes (INM) of a number of ionic melts are examined in the light of recent proposals which connect them to diffusion and to the strong/liquid character of the fluid. Separate INM density-of-states may be found for each ionic species. A linear relationship between the temperature dependence of the fraction of INMs which are unstable (fu) and that of the diffusion coefficient of each species has been found. The shapes of the single-mode potential energy curves of the fluid along INM eigenvectors are examined. The results do not support a general significance for "double-well" modes as the only ones involved in diffusion. An alternative explanation of how single or double well features develop on the single-mode potential curves is proposed. The shape of the unstable INM density-of-states reflects the character of the ionic motion: a crossover from |ω|exp(−Bω2) to |ω|exp(−Bω4) occurs as the ionic motion becomes increasingly hindered. Both behaviors, which have been reported previously for the Lennard-Jones atomic fluid at normal liquid and supercooled conditions, respectively, can occur simultaneously in a single melt for each ionic species. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475722
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