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  • 1. Luo, Yi
    et al.
    Norman, P.
    Macak, P.
    KTH.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Nonlinear optical susceptibilities of fullerenes in the condensed phase2000In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, no 4, p. 3060-3066Article in journal (Refereed)
    Abstract [en]

    We present results for nonlinear optical susceptibilities of fullerenes, including C-60, C-70, and C-84, in the condensed phase from large-scale nb initio calculations using self-consistent reaction field theory and an analytical local-field method. It is shown that the intermolecular polarization interaction has significant effects on the nonlinear properties of the fullerenes, and that, in some contrast to other organic species, nondipolar contributions to this interaction are important. Based on the theoretical and experimental results for the polarizability of C-60 in the gas phase, a general local-field factor for C-60 film has been obtained, which is found to be quite different from the classical Lorenz-Lorentz local-field factor. The calculated and experimental nonlinear optical susceptibilities of C-60 are in good agreement provided the comparison is made on the same basis, viz at nonresonant frequencies and considering the relevant macroscopic quantities. The dielectric and density dependence of the nonlinear optical susceptibilities of C-70 are discussed.

  • 2.
    Macak, Peter
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Tsushima, Satoru
    Wahlgren, Ulf
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    A theoretical study of the fluoride exchange between UO2F+(aq) and UO22+(aq)2006In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 30, p. 3638-3646Article in journal (Refereed)
    Abstract [en]

    Experimental data on the thermodynamics and reaction mechanism of the inner-sphere. uoride exchange reaction (UO22+)-O-17 + UO2F+ reversible arrow (UO2F+)-O-17 + UO22+ have been compared with different intimate reaction mechanisms using quantum chemical methods. Two models have been tested that start from the outer sphere complexes, (H2O)[UAO2F(OH2)(4)(+)] center dot center dot center dot [UBO2(OH2)(5)(2+)] and [UAO2F(OH2)(4)(+)] center dot center dot center dot [UBO2(OH2)(5)(2+)]; the geometry and energies of the intermediates and transition states along possible reaction pathways have been calculated using different ab initio methods, SCF, B3LYP and MP2. Both the experimental data and the theoretical results suggest that the. uoride exchange takes place via the formation and breaking of a U - F - U bridge that is the rate determining step. The calculated activation enthalpy Delta H-not equal = 30.9 kJ mol(-1) is virtually identical to the experimental value 31 kJ mol(-1); however this agreement may be a coincidence as we do not expect a larger accuracy than 10 kJ mol(-1) with the methods used. The calculations show that the. uoride bridge is formed as an insertion of UAO2F(OH2)(4)(+) into UBO2(OH2)(5)(2+) followed by a subsequent transfer of water from the first to the second coordination sphere of U-B.

  • 3.
    Privalov, Timofei
    et al.
    KTH, Superseded Departments, Chemistry.
    Macak, Peter
    KTH, Superseded Departments, Physics.
    Schimmelpfennig, B.
    Fromager, E.
    Grenthe, I.
    Wahlgren, Ulf
    KTH, Superseded Departments, Physics.
    Electron transfer in uranyl(VI)-uranyl(V) complexes in solution2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 31, p. 9801-9808Article in journal (Refereed)
    Abstract [en]

    The rates and mechanisms of the electron self-exchange between U(V) and U(VI) in solution have been studied with quantum chemical methods. Both outer-sphere and inner-sphere mechanisms have been investigated; the former for the aqua ions, the latter for binuclear complexes containing hydroxide, fluoride, and carbonate as bridging ligand. The calculated rate constant for the self-exchange reaction UO2+(aq) + UO22+(aq)UO22+(aq) + UO2+(aq), at 25 degreesC, is k = 26 M-1 s(-1). The lower limit of the rate of electron transfer in the inner-sphere complexes is estimated to be in the range 2 x 10(4) to 4 x 10(6) M-1 s(-1), indicating that the rate for the overall exchange reaction may be determined by the rate of formation and dissociation of the binuclear complex. The activation energy for the outer-sphere model calculated from the Marcus model is nearly the same as that obtained by a direct calculation of the precursor- and transition-state energy. A simple model with one water ligand is shown to recover 60% of the reorganization energy. This finding is important because it indicates the possibility to carry out theoretical studies of electron-transfer reactions involving M3+ and M4+ actinide species that have eight or nine water ligands in the first coordination sphere.

  • 4. Vallet, V.
    et al.
    Macak, Peter
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Wahlgren, U.
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Actinide chemistry in solution, quantum chemical methods and models2006In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 115, no 2-3, p. 145-160Article in journal (Refereed)
    Abstract [en]

    Theoretical modeling of actinide complexes requires access to structural parameters, information on electronic, vibration and rotation energy levels and thermodynamics properties. This article presents a critical review of theoretical studies of actinide chemistry in gas-phase and in solution and a comparison with experimental data in order to assess the applicability and accuracy by which various electronic structure theories can predict the required quantities. The quality of the basis set, the importance of electron correlation, the description of solute-solvent interactions is discussed in some detail.

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