| 491. |
- Luo, Yi, et al.
(författare)
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Solvent-induced two-photon absorption of a push-pull molecule
- 2000
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 104:20, s. 4718-4722
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Tidskriftsartikel (refereegranskat)abstract
- Solvent-induced two-photon absorption cross sections are calculated for a push-pull molecule in solutions using both self-consistent reaction field and internal finite field approaches. It is shown analytically and numerically that the results from the two methods can be connected through induced local reaction field factors. The two-photon cross sections of the studied push-pull polyene are found to be rather insensitive to the choice of cavity shape. The solvent dependence of the two-photon absorption displays a pattern different from that of the first hyperpolarizability.
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| 492. |
- Löytynoja, Tuomas, 1987-
(författare)
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Quantum and quantum-classical calculations of core-ionized molecules in varied environments
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Computational quantum chemistry methods have been applied in two particular cases: to provide insight to photoionization induced fragmentation of HgBr2 and HgCl2 molecules, and to study core-electron binding energies and chemical shifts of molecules in liquid, surface adsorbed and polymeric environments in the framework of quantum mechanics/molecular mechanics (QM/MM). In the photodissociation studies the computational work is based on the relativistic Dirac equation as the systems present strong spin-orbit interaction affecting the fragmentation processes. In the QM/MM studies of ethanol-water mixtures and molecules physisorbed on silver surfaces the structures are provided by classical molecular dynamics simulations to analyze the distribution of the binding energies of core-orbitals and effects of their surroundings. In the case of polymethyl methacrylate polymer the impact of a QM-MM boundary and a polymeric environment are studied. The theoretical backgrounds of the computational methods applied and the obtained results are discussed.
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| 493. |
- Löytynoja, T., et al.
(författare)
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Quantum-classical calculations of X-ray photoelectron spectra of polymers-Polymethyl methacrylate revisited
- 2017
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 146:12
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we apply quantum mechanics/molecular mechanics (QM/MM) approach to predict core-electron binding energies and chemical shifts of polymers, obtainable via X-ray photoelectron spectroscopy (XPS), using polymethyl methacrylate as a demonstration example. The results indicate that standard parametrizations of the quantum part (basis sets, level of correlation) and the molecular mechanics parts (decomposed charges, polarizabilities, and capping technique) are sufficient for the QM/MM model to be predictive for XPS of polymers. It is found that the polymer environment produces contributions to the XPS binding energies that are close to monotonous with the number of monomer units, totally amounting to approximately an eV decrease in binding energies. In most of the cases, the order of the shifts is maintained, and even the relative size of the differential shifts is largely preserved. The coupling of the internal core-hole relaxation to the polymer environment is found to be weak in each case, amounting only to one or two tenths of an eV. The main polymeric effect is actually well estimated already at the frozen orbital level of theory, which in turn implies a substantial computational simplification. These conclusions are best represented by the cases where the ionized monomer and its immediate surrounding are treated quantum mechanically. If the QM region includes only a single monomer, a couple of anomalies are spotted, which are referred to the QM/MM interface itself and to the neglect of a possible charge transfer.
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| 494. |
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| 495. |
- Löytynoja, Tuomas, et al.
(författare)
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Quantum Mechanics/Molecular Mechanics Modeling of Photoelectron Spectra : The Carbon 1s Core-Electron Binding Energies of Ethanol-Water Solutions
- 2014
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:46, s. 13217-13225
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Tidskriftsartikel (refereegranskat)abstract
- Using ethanolwater solutions as illustration, we demonstrate the capability of the hybrid quantum mechanics/molecular mechanics (QM/MM) paradigm to simulate core photoelectron spectroscopy: the binding energies and the chemical shifts. An integrated approach with QM/MM binding energy calculations coupled to preceding molecular dynamics sampling is adopted to generate binding energies averaged over the solutesolvent configurations available at a particular temperature and pressure and thus allowing for a statistical assessment with confidence levels for the final binding energies. The results are analyzed in terms of the contributions in the molecular mechanics modelelectrostatic, polarization, and van der Waalswith atom or bond granulation of the corresponding MM charge and polarizability force-fields. The role of extramolecular charge transfer screening of the core-hole and explicit hydrogen bonding is studied by extending the QM core to cover the first solvation shell. The results are compared to those obtained from pure electrostatic and polarizable continuum models. Particularly, the dependence of the carbon 1s binding energies with respect to the ethanol concentration is studied. Our results indicate that QM/MM can be used as an all-encompassing model to study photoelectron binding energies and chemical shifts in solvent environments.
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| 496. |
- Macak, P., et al.
(författare)
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Modeling of dynamic molecular solvent properties using local and cavity field approaches
- 2000
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 112:4, s. 1868-1875
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Tidskriftsartikel (refereegranskat)abstract
- Current models of solvent properties using cavity reaction field methods are analyzed and categorized in two groups according to the use of local fields or cavity fields as the perturbing fields. Analytical connections between the two approaches are derived.
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| 497. |
- Macak, P., et al.
(författare)
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Simulations of vibronic profiles in two-photon absorption
- 2000
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 330:04-mar, s. 447-456
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Tidskriftsartikel (refereegranskat)abstract
- We propose and evaluate an approach for simulating vibronic profiles in two-photon absorption (TPA) of polyatomic molecules accounting for both Franck-Condon and Herzberg-Teller couplings. A linear coupling scheme is implemented in which the multi-dimensional vibronic coupling constants are obtained from ground state frequencies and normal coordinates and excited state energy gradients evaluated at the ground state equilibrium geometry. Applications on charge-transfer monomer and dimer molecules based on trans-polyene indicate the importance of vibrational TPA profiles in experimental predictions and comparisons.
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| 498. |
- Macak, Peter, et al.
(författare)
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Two-photon excitations in molecules
- 2003
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Ingår i: Non-linear optical responses of molecules,solids and liquids: Methods and applications. - : Plenum Publishing.
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Bokkapitel (refereegranskat)abstract
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| 499. |
- Magnuson, Martin, et al.
(författare)
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Competition between decay and dissociation of core-excited carbonyl sulfide studied by x-ray scattering
- 1999
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 59:6, s. 4281-4287
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Tidskriftsartikel (refereegranskat)abstract
- We show evidence of dissociation during resonant inelastic soft x-ray scattering Carbon and oxygen K-shell and sulfur L-shell resonant and nonresonant x-ray emission spectra were measured using monochromatic synchrotron radiation for excitation and ionization. After sulfur L-2,L-3-->pi*, sigma* excitation, atomic lines are observed in the emission spectra as a consequence of competition between de-excitation and dissociation. In contrast thr carbon and oxygen spectra show weaker line-shape variations and no atomic Lines. The spectra are compared to results from ab initio calculations. The discussion of the dissociation paths is based on calculated potential energy surfaces and atomic transition energies.
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| 500. |
- Makris, Georgios, 1977-
(författare)
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Suicide Seasonality : Theoretical and Clinical Implications
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Although suicide seasonality has been well-documented, surprisingly little is known about its underlying mechanisms.Methods: In this thesis, data from three Swedish registers (Cause of Death Register, National Patient Register, Prescribed Drugs Register) and data from the Swedish Meteorological and Hydrological Institute were used.In Study I, the amplitude of suicide seasonality was estimated in completed suicides in 1992-2003 in individuals with different antidepressant medications or without antidepressants.In Study II, monthly suicide and sunshine data from 1992-2003 were used to examine the association between suicide and sunshine in groups with and without antidepressants.In Study III, the relationship between season of initiation of antidepressant treatment and the risk of suicidal behavior was explored in patients with a new treatment episode with antidepressant medication.In Study IV, the complex association between sunshine, temperature and suicidal behavior was investigated in patients with a new treatment episode with an antidepressant in two exposure windows (1-4 and 5-8 weeks) before the event.Findings: Study I: Higher suicide seasonality was found in individuals treated with selective serotonin reuptake inhibitors (SSRIs) compared with those given a different antidepressant treatment or those without any antidepressant treatment.Study II: In individuals treated with SSRIs, there was a positive association between sunshine and suicide, with the association stronger in men treated with SSRIs compared with men treated with other antidepressants. An effect modification by age was observed.Study III: The elderly (65+) had a higher risk of suicide when initiating antidepressant treatment in summer and a higher risk of suicide attempt when starting antidepressant therapy in spring and summer. Younger patients (0-24) demonstrated a higher risk of suicide attempt when treatment was initiated in autumn.Study IV: In the elderly (65+), a harmful association was observed between the risk of suicide attempt and the average daily temperature during the four weeks before the suicide attempt, as well as with average daily sunshine during both exposure windows (1-4 and 5-8 weeks) before the suicide attempt.Significance: Our results provide epidemiological support for the role of the serotonergic system in seasonality of suicide in which both medication and climate may be involved.
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