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  • 1.
    Fahleson, Tobias
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Derivation and application of response functions for nonlinear absorption and dichroisms2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is titled ’Derivation and application of response functions for nonlinear absorption and dichroisms’ and was written by Tobias Fahleson at the Division of Theoretical Chemistry & Biology at KTH Royal Institute of Technology in Sweden. It explores and expands upon theoretical means of quantifying a number of nonlinear spectroscopies, including two-photon absorption, resonant inelastic x-ray scattering, Jones birefringence, and magnetic circular dichroism. Details are provided for the derivation and program implementation of complex-valued (damped) cubic response functions that have been implemented in the quantum chemistry package DALTON [1], based on working equations formulated for an approximate-state wave function. This is followed by an assessment of the implementation. It is demonstrated how two-photon absorption (TPA) can be described either through second-order transition moments or the damped cubic response function. A set of illustrative TPA profiles are produced for smaller molecules. In addition, resonant inelastic x-ray scattering (RIXS) is explored in a similar manner as two-photon absorption. It is shown for small systems how RIXS spectra may be obtained using a reduced form of the cubic response function. Linear birefringences are investigated for noble gases, monosubstituted benzenes, furan homologues, and liquid acetonitrile. Regarding the noble gases, the Jones effect is shown to be proportional to a power series with respect to atomic radial sizes. For monosubstituted benzenes, a linear relation between the Jones birefringence and the empirical para-Hammett constant as well as the permanent electric dipole moment is presented. QM/MM protocols are applied for a pure acetonitrile liquid, including polarizable embedding and polarizable-density embedding models. The final chapter investigates magnetically induced circular dichroism (MCD). A question regarding relative stability of the first set of excited states for DNA-related molecular systems is resolved through MCD by exploiting the signed nature of circular dichroisms. Furthermore, to what extent solvent contributions affect MCD spectra and the effect on uracil MCD spectrum due to thionation is studied.

  • 2.
    Fahleson, Tobias
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Norman, Patrick
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Resonant-convergent second-order nonlinear response functions at the levels of Hartree-Fock and Kohn-Sham density functional theory2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 14, article id 144109Article in journal (Refereed)
    Abstract [en]

    The second-order nonlinear (or cubic) response function is derived from the Ehrenfest theorem with inclusion made of the finite lifetimes of the excited states, representing the extension of the derivation of the quadratic response function in the same framework [P. Norman et al., J. Chem. Phys. 123, 194103 (2005)]. The resulting damped response functions are physically sound and converging also in near-resonance and resonance regions of the spectrum. Being an accurate approximation for small complex frequencies (defined as the sum of an optical frequency and an imaginary damping parameter), the polynomial expansion of the complex cubic response function in terms of the said frequencies is presented and used to validate the program implementation. In terms of approximate state theory, the computationally tractable expressions of the damped cubic response function are derived and implemented at the levels of Hartree-Fock and Kohn-Sham density functional theory. Numerical examples are provided in terms of studies of the intensity-dependent refractive index of para-nitroaniline and the two-photon absorption cross section of neon. For the latter property, a numerical comparison is made against calculations of the square of two-photon matrix elements that are identified from a residue analysis of the resonance-divergent quadratic response function.

  • 3.
    Fahleson, Tobias
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Olsen, Jogvan Magnus Haugaard
    Norman, Patrick
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Rizzo, Antonio
    A QM/MM and QM/QM/MM study of Kerr, Cotton-Mouton and Jones linear birefringences in liquid acetonitrile2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 5, p. 3831-3840Article in journal (Refereed)
    Abstract [en]

    QM/MM and QM/QM/MM protocols are applied to the ab initio study of the three linear birefringences Kerr, Cotton-Mouton, and Jones, as shown by acetonitrile in the gas and pure liquid phases. The relevant first-order properties as well as linear, quadratic, and cubic frequency-dependent response functions were computed using time-dependent Kohn-Sham density-functional theory with use of the standard CAM-B3LYP functional. In the liquid phase, a series of room temperature (293.15 K) molecular dynamics snapshots were selected, for which averaged values of the observables were obtained at an optical wavelength of 632.8 nm. The birefringences were computed for electric and magnetic induction fields corresponding to the laboratory setup previously employed by T. Roth and G. L. J. A. Rikken in Phys. Rev. Lett., 2000, 85, 4478. Under these conditions, acetonitrile is shown to exhibit a weak Jones response-in fact roughly 6.5 times smaller than the limit of detection of the apparatus employed in the measurements mentioned above. A comparison is made with the corresponding gas-phase results and an assessment is made of the index of measurability, estimating the degree of overlap of the three birefringences in actual measurements. For acetonitrile, it is shown that this index is a factor of 3.6 and 6.7 larger than that of methylcyclopentadienyl-Mn-tricarbonyl and cyclohexadienyl-Fe-tricarbonyl, respectively-two compounds reported in Phys. Rev. Lett., 2000, 85, 4478 to exhibit a strong Jones signal.

  • 4. Fahleson, Tobias
    et al.
    Olsen, Jógvan Magnus Haugaard
    Norman, Patrick
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Rizzo, Antonio
    A QM/MM and QM/QM/MM study of Kerr, Cotton--Mouton and Jones linear birefringences in liquid acetonitrile2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084Article in journal (Refereed)
    Abstract [en]

    QM/MM and QM/QM/MM protocols are applied to the ab initio study of the three linear bire-fringences Kerr, Cotton–Mouton, and Jones, as shown by acetonitrile in the gas and pureliquid phases. The relevant first-order properties as well as linear, quadratic, and cubicfrequency-dependent response functions were computed using time-dependent Kohn–Shamdensity-functional theory with use of the standard CAM-B3LYP functional. In the liquid phase,a series of room temperature (293.15 K) molecular dynamics snapshots were selected, for whichaveraged values of the observables were obtained at an optical wavelength of 632.8 nm. Thebirefringences were computed for electric and magnetic induction fields corresponding to the lab-oratory setup previously employed by Roth and Rikken in Phys. Rev. Lett. 85, 4478, (2000).Under these conditions, acetonitrile is shown to exhibit a weak Jones response — in fact roughly6.5 times smaller than the limit of detection of the apparatus employed in the measurementsmentioned above. A comparison is made with the corresponding gas-phase results and an as-sessment is made of the index of measureability, estimating the degree of overlap of the threebirefringences in actual measurements. For acetonitrile, it is shown that this index is a factorof 3.6 and 6.7 larger than that of methylcyclopentadienyl-Mn-tricarbonyl and cyclohexadienyl-Fe-tricarbonyl, respectively — two compounds reported in Phys. Rev. Lett. 85, 4478, (2000) to exhibita strong Jones signal.

  • 5. Martinez-Fernandez, L.
    et al.
    Fahleson, Tobias
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Norman, Patrick
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Santoro, F.
    Coriani, S.
    Improta, R.
    Optical absorption and magnetic circular dichroism spectra of thiouracils: a quantum mechanical study in solution2017In: Photochemical and Photobiological Sciences, ISSN 1474-905X, E-ISSN 1474-9092, Vol. 16, no 9, p. 1415-1423Article in journal (Refereed)
    Abstract [en]

    The excited electronic states of 2-thiouracil, 4-thiouracil and 2,4-dithiouracil, the analogues of uracil where the carbonyl oxygens are substituted by sulphur atoms, have been investigated by computing the magnetic circular dichroism (MCD) and one-photon absorption (OPA) spectra at the time-dependent density functional theory level. Special attention has been paid to solvent effects, included by a mixed discrete/continuum model, and to determining how our results depend on the adopted DFT functional (CAM-B3LYP and B3LYP). Whereas including solvent effects does not dramatically impact the MCD and OPA spectra, though improving the agreement with the experimental spectra, the performances of CAM-B3LYP and B3LYP are remarkably different. CAM-B3LYP captures well the effect of thionation on the uracil excited states and provides spectra in good agreement with the experiments, whereas B3LYP shows some deficiency in describing 2-TU and 2,4-DTU spectra, despite being more accurate than CAM-B3LYP for 4-TU.

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