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Fahleson, Tobias
Publications (6 of 6) Show all publications
Fahleson, T., Ågren, H. & Norman, P. (2016). A Polarization Propagator for Nonlinear X-ray Spectroscopies. Journal of Physical Chemistry Letters, 7(11), 1991-1995
Open this publication in new window or tab >>A Polarization Propagator for Nonlinear X-ray Spectroscopies
2016 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 11, p. 1991-1995Article in journal (Refereed) Published
Abstract [en]

A complex polarization propagator approach has been developed to third order and implemented in density functional theory (DFT), allowing for the direct calculation of nonlinear molecular properties in the X-ray wavelength regime without explicitly addressing the excited-state manifold. We demonstrate the utility of this propagator method for the modeling of coherent near-edge X-ray two-photon absorption using, as an example, DFT as the underlying electronic structure model. Results are compared with the corresponding near edge X-ray absorption fine structure spectra, illuminating the differences in the role of symmetry, localization, and correlation between the two spectroscopies. The ramifications of this new technique for nonlinear X-ray research are briefly discussed.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2016
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-130066 (URN)10.1021/acs.jpclett.6b00750 (DOI)000377239200009 ()27159130 (PubMedID)
Note

Funding Agencies|Knut and Alice Wallenberg Foundation [KAW-2013.0020]; Swedish Research Council [621-2014-4646]

Available from: 2016-07-06 Created: 2016-07-06 Last updated: 2017-11-28
Fahleson, T. (2015). Development and characterization of damped cubic response functions with application to two-photon absorption. (Licentiate dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Development and characterization of damped cubic response functions with application to two-photon absorption
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Molecular response to electromagnetic fields - static or optical - within a framework of perturbation theory diverges close to resonance with molecular transitionen energies, and need work-around solutions for real-valued response functions. This licentiate thesis deals with nonlinear response, with focus being on cubic polarizaibilities, and outlines the underlying mathematics for exact-state and approximatestate, complex-valued response functions applicable to quantum chemical computation. Such a complex-valued response theory is commonly known as dampedresponse theory, for which the response functions consists of a real and an imaginary component, each of them representing various spectroscopies in nature. In addition to the mathematics, the formulas have been implemented in the quantum chemical package DALTON, and several tests determining the integrity of the implementation has been conducted.

The fourth and final major part of the thesis is concerned with applied nonlinear response theory, including not only cubic response functions, but also quadratic and linear response functions, some of which are of the more exotic character. Three spectroscopies have been investigated for small and medium-sized organic molecules and the neon atom: two-photon absorption (TPA), Jones birefringence (JB), and magnetic circular dichroism (MCD).

The TPA part is a simple demonstration of capability of the damped cubic response code, for which neon is the example system. Perfect agreement is shown for the Ehrenfest approach and an independent implementation based on the quasienergy formalism.

JB is an optical eect in which induced refractive anisotropy, by means of external electric and magnetic static elds, results in ellipticity of linearly polarized light beams. This part mainly discuss implications from a paper which the current author took part in. The paper ultimately attempts to indentify the general observable strength of the effect, and coincidentaly pin-point some particular system suitable for experiments. Among other finds, JB is found to be correlated to the electric dipole moment, and for monosubstituted benzenes, the para-Hammett constant.

Finally, MCD is discussed based on three papers in which the present author is included. The elegant MCD solution to broad absorption peaks, for which it is desired to distinguish individual states, is demonstrated on adenine and three additional purine derivatives. A drawn out debate regarding relative stability of certain low-lying states could be settled by this method. Furthermore, appropriate description of solvation environment in conjunction with the exchange-correlation functionals B3LYP and CAM-B3LYP is investigated on purine and pyrimidine derivatives. CAM-B3LYP is found to be superior in terms of general prole shapes, while results regarding solvation model are rather inconclusive, although the results suggests some level of solvation model is appropriate, such as a polarizable continuum model or explicit solvation molecules.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. p. 67
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1742
National Category
Theoretical Chemistry Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-123972 (URN)978-91-7685-844-8 (ISBN)
Supervisors
Available from: 2016-01-15 Created: 2016-01-15 Last updated: 2016-01-15Bibliographically approved
Fahleson, T., Kauczor, J., Norman, P., Santoro, F., Improta, R. & Coriani, S. (2015). TD-DFT Investigation of the Magnetic Circular Dichroism Spectra of Some Purine and Pyrimidine Bases of Nucleic Acids. Journal of Physical Chemistry A, 119(21), 5476-5489
Open this publication in new window or tab >>TD-DFT Investigation of the Magnetic Circular Dichroism Spectra of Some Purine and Pyrimidine Bases of Nucleic Acids
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2015 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 21, p. 5476-5489Article in journal (Refereed) Published
Abstract [en]

We present a computational study of the Magnetic circular dichroism (MCD) spectra in the 200-300 nm wavelength region of purine and its derivative hypoxanthine, as well as of the pyrimidine bases of nucleic acids uracil,thymine, and cytosine, Using the B3LYP and CAM-B3LYP functionals. Solvent effects, are investigated within the polarizable continuum model and by inclusion of explicit water molecules. In, general; the computed spectra are found to be in good agreement with the experimental ones, aprt from some overall blue shifts. Both the pseudo-A term shape of the MCD spectra of the purines and the B term shape of the spectra of pyrimidine base are reproduced. Our calculations also correctly reproduce the reversed phase of the MCD bands in purine compared to,that of its derivatives present in nucleic acids. Solvent effects are sizable and system specific,but they do not in general alter the qualitative shape of the spectra. The bands are dominated the-bright pi -greater than pi* transitions; and our calculations in solution nicely reproduce theft energy differences, improving the estimates obtained in the gas phase. Shoulders are predicted for purine and uracil due to n -greater than pi* excitations, but they are too weak to be observed in the. experiment.

Place, publisher, year, edition, pages
American Chemical Society, 2015
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:liu:diva-119800 (URN)10.1021/jp512468k (DOI)000355495100043 ()25648759 (PubMedID)
Note

Funding Agencies|PRIN [2010ERFKXL_008]; University of Trieste [CHIM02-Ricerca]

Available from: 2015-06-26 Created: 2015-06-26 Last updated: 2017-12-04
Santoro, F., Improta, R., Fahleson, T., Kauczor, J., Norman, P. & Coriani, S. (2014). Relative Stability of the L-a and L-b Excited States in Adenine and Guanine: Direct Evidence from TD-DFT Calculations of MCD Spectra. Journal of Physical Chemistry Letters, 5(11), 1806-1811
Open this publication in new window or tab >>Relative Stability of the L-a and L-b Excited States in Adenine and Guanine: Direct Evidence from TD-DFT Calculations of MCD Spectra
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2014 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 5, no 11, p. 1806-1811Article in journal (Refereed) Published
Abstract [en]

The relative position of L-a and L-b pi pi* electronic states in purine nucleobases is a much debated topic, since it can strongly affect our understanding of their photoexcited dynamics. To assess this point, we calculated the absorption and magnetic circular dichroism (MCD) spectra of adenine, guanine, and their nucleosides in gas-phase and aqueous solution,. exploiting recent developments in MCD computational technology within time-dependent density functional theory. MCD spectroscopy allows us to resolve the intense S-0 -greater than L-a transition from the weak S-0 -greater than L-b transition. The spectra obtained in water solution, by using B3LYP and CAM-B3LYP functionals and describing solvent effect by cluster models and by the polarizable continuum model (PCM), are in very good agreement with the experimental counterparts, thus providing direct and unambiguous evidence that the energy ordering predicted by TD-DFT, L-a less than L-b, is the correct one.

Place, publisher, year, edition, pages
American Chemical Society, 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-108796 (URN)10.1021/jz500633t (DOI)000337012500005 ()
Available from: 2014-07-07 Created: 2014-07-06 Last updated: 2017-12-05
Fahleson, T., Norman, P., Coriani, S., Rizzo, A. & Rikken, G. L. (2013). A density functional theory study of magneto-electric Jones birefringence of noble gases, furan homologues, and mono-substituted benzenes. Journal of Chemical Physics, 139(19), 194311
Open this publication in new window or tab >>A density functional theory study of magneto-electric Jones birefringence of noble gases, furan homologues, and mono-substituted benzenes
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2013 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 139, no 19, p. 194311-Article in journal (Refereed) Published
Abstract [en]

We report on the results of a systematic ab initio study of the Jones birefringence of noble gases, of furan homologues, and of monosubstituted benzenes, in the gas phase, with the aim of analyzing the behavior and the trends within a list of systems of varying size and complexity, and of identifying candidates for a combined experimental/theoretical study of the effect. We resort here to analytic linear and nonlinear response functions in the framework of time-dependent density functional theory. A correlation is made between the observable (the Jones constant) and the atomic radius for noble gases, or the permanent electric dipole and a structure/chemical reactivity descriptor as the para Hammett constant for substituted benzenes.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-102851 (URN)10.1063/1.4830412 (DOI)000327714900024 ()
Note

Funding Agencies|EuroMagNET II, under EU|228043|Swedish Research Council|621-2010-5014|Italian Ministero dellIstruzione, Universita e Ricerca|2009C28YBF_001|National Supercomputer Centre (NSC), Sweden||Italian CINECA||

Available from: 2014-01-07 Created: 2014-01-02 Last updated: 2017-12-06
Fahleson, T. & Norman, P.Resonant-convergent cubic response function in the random-phase approximation with application to two-photon absorption on neon in the ultraviolet-visible region.
Open this publication in new window or tab >>Resonant-convergent cubic response function in the random-phase approximation with application to two-photon absorption on neon in the ultraviolet-visible region
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Damped cubic response functions are presented for exact-state and approximate-state methods eligible for quantum chemical computational applications. Proof of proper implementation is given, accompanied by a two-photon absorption example on neon in the ultraviolet-visible spectral region. The method accurately distinguish one- and two-photon resonances and exhibits spot-on agreement with other approaches.

Keywords
Hyperpolarizability, damped response, cubic response
National Category
Theoretical Chemistry Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-123971 (URN)
Available from: 2016-01-15 Created: 2016-01-15 Last updated: 2016-01-15Bibliographically approved
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