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- Fahleson, Tobias, 1989-, et al.
(author)
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A QM/MM and QM/QM/MM study of Kerr, Cotton--Mouton and Jones linear birefringences in liquid acetonitrile
- 2017
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084.
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Journal article (peer-reviewed)abstract
- 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.
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| 2. |
- Fahleson, Tobias, 1989-
(author)
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Derivation and application of response functions for nonlinear absorption and dichroisms
- 2018
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Doctoral thesis (other academic/artistic)abstract
- 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.
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