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Collective Excitation Dynamics in Molecular Aggregates

Dahlbom, Mats LU (2002)
Abstract (Swedish)
Popular Abstract in Swedish

Den här avhandlingen är framlagd i ämnet kemisk fysik. Kemisk fysik är ett mycket stort forskningsområde, som innefattar fenomen allt ifrån vibrationer i molekylära bindningar till betydligt större fenomen, som till exempel energi och elektrontransport i den naturliga fotosyntesen. Fotosyntesen är naturens mest betydelsefulla process. Den driver i princip alla växter, som i sin tur är föda för alla jordens djur, inklusive oss människor. Detta är något vi alla känner väl till ifrån skolan och det är säkerligen ingen överraskning för någon att denna process till stora delar är mycket effektiv. Det är dock inte bara gröna växter som utnyttjar fotosyntesen utan även många planktonarter och bakterier... (More)
Popular Abstract in Swedish

Den här avhandlingen är framlagd i ämnet kemisk fysik. Kemisk fysik är ett mycket stort forskningsområde, som innefattar fenomen allt ifrån vibrationer i molekylära bindningar till betydligt större fenomen, som till exempel energi och elektrontransport i den naturliga fotosyntesen. Fotosyntesen är naturens mest betydelsefulla process. Den driver i princip alla växter, som i sin tur är föda för alla jordens djur, inklusive oss människor. Detta är något vi alla känner väl till ifrån skolan och det är säkerligen ingen överraskning för någon att denna process till stora delar är mycket effektiv. Det är dock inte bara gröna växter som utnyttjar fotosyntesen utan även många planktonarter och bakterier nyttjar den. De initiala stegen i fotosyntesen kan i princip beskrivas som en fler-stegs process; (i) infångande av soljus, (ii) transport av den infångade energin och slutligen (iii) den av energin initierade transport av en elektron genom cellmembranet. Vi har studerat egenskaperna hos de grundläggande energipaket som antennsystemen innehåller efter att de har blivit belysta med ljus. Dessa ljusinsamlande antenner består av pigment molekyler. På grund av den starka kopplingen mellan dessa byggstenar så kommer energipaketen att vara ”utsmetade” ¨over en betydande del av antennen. Den här avhandlingen berör de första momenten av energitransporten i den naturliga fotosyntesen och den teoretiska beskrivningen av de grundläggande excitationernas egenskaper och dynamik i antennkomplexen. Avhandlingen innehaller lika delar metod utveckling och applikationer av dessa metoder på fotosyntetiska antenn och modell-system. (Less)
Abstract
The aim of this thesis is to study collective excitation dynamics in molecular aggregates. Half of the work presented here is method development and the remainder is application of these methods to several di.erent molecular aggregates. In the first two papers, the pump-probe signal was derived using the Green function approach of the optical response functions and formulated in the Doorway-Window representation. This method was applied to the B850 aggregate of the purple bacteria, Rhodobacter sphaeroides and compared with recent experimental results. The steady-state absorption as well as the thermalized pump-probe spectra were in good agreement with the experimental data for a given parameter set. Furthermore, the temporal evolution of... (More)
The aim of this thesis is to study collective excitation dynamics in molecular aggregates. Half of the work presented here is method development and the remainder is application of these methods to several di.erent molecular aggregates. In the first two papers, the pump-probe signal was derived using the Green function approach of the optical response functions and formulated in the Doorway-Window representation. This method was applied to the B850 aggregate of the purple bacteria, Rhodobacter sphaeroides and compared with recent experimental results. The steady-state absorption as well as the thermalized pump-probe spectra were in good agreement with the experimental data for a given parameter set. Furthermore, the temporal evolution of the transient absorption spectra was also well described for the same parameter set. The concept of exciton delocalization was addressed using this method and several theoretical estimations were discussed and compared with each other. Furthermore, the time evolution and dependency of the initial preparation were studied and compared with different experimental techniques. In the second part, the excitation dynamics in molecular aggregates was studied using the surface hopping technique. This method incorporates coupling to the nuclear coordinates explicitly and treats the nuclear system classically. The third and the forth paper included in this thesis, develops the surface hopping method and the simulations were made for model aggregates. The fifth paper introduces an analytical version of the previously presented surface hopping model. In the last included paper, this method was applied to the B850 antenna complex of Rhodobacter sphaeroides with parameters extracted from a realistic spectral density distribution. A number of explicit harmonic oscillators were used to describe the molecular vibrations. Special attention was directed to the nonlinear dependence of the excitonic potential energy surfaces and the exciton-vibrational feedback term. Polaron formation, migration and self-trapping was shown to occur for certain parameter sets. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Professor Knoester, J., Institute for Theoretical Physics,University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands.
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Chemistry, Kemi, Fysik, Physics, computational methods, photosynthesis, femtosecond spectroscopy, Exciton, Polaron
pages
130 pages
publisher
Department of Chemical Physics, Lund University
defense location
Lecture Hall B, Chemisty Center, Getingevägen 60, Lund, Sweden
defense date
2002-02-01 14:15
ISBN
91-7874-174-2
language
English
LU publication?
yes
id
4aeefee1-b3fe-4b80-ab45-adfbc0557174 (old id 464273)
date added to LUP
2007-10-14 14:52:58
date last changed
2016-09-19 08:45:07
@misc{4aeefee1-b3fe-4b80-ab45-adfbc0557174,
  abstract     = {The aim of this thesis is to study collective excitation dynamics in molecular aggregates. Half of the work presented here is method development and the remainder is application of these methods to several di.erent molecular aggregates. In the first two papers, the pump-probe signal was derived using the Green function approach of the optical response functions and formulated in the Doorway-Window representation. This method was applied to the B850 aggregate of the purple bacteria, Rhodobacter sphaeroides and compared with recent experimental results. The steady-state absorption as well as the thermalized pump-probe spectra were in good agreement with the experimental data for a given parameter set. Furthermore, the temporal evolution of the transient absorption spectra was also well described for the same parameter set. The concept of exciton delocalization was addressed using this method and several theoretical estimations were discussed and compared with each other. Furthermore, the time evolution and dependency of the initial preparation were studied and compared with different experimental techniques. In the second part, the excitation dynamics in molecular aggregates was studied using the surface hopping technique. This method incorporates coupling to the nuclear coordinates explicitly and treats the nuclear system classically. The third and the forth paper included in this thesis, develops the surface hopping method and the simulations were made for model aggregates. The fifth paper introduces an analytical version of the previously presented surface hopping model. In the last included paper, this method was applied to the B850 antenna complex of Rhodobacter sphaeroides with parameters extracted from a realistic spectral density distribution. A number of explicit harmonic oscillators were used to describe the molecular vibrations. Special attention was directed to the nonlinear dependence of the excitonic potential energy surfaces and the exciton-vibrational feedback term. Polaron formation, migration and self-trapping was shown to occur for certain parameter sets.},
  author       = {Dahlbom, Mats},
  isbn         = {91-7874-174-2},
  keyword      = {Chemistry,Kemi,Fysik,Physics,computational methods,photosynthesis,femtosecond spectroscopy,Exciton,Polaron},
  language     = {eng},
  pages        = {130},
  publisher    = {ARRAY(0xb92b1b0)},
  title        = {Collective Excitation Dynamics in Molecular Aggregates},
  year         = {2002},
}