Molecular Quadratic Response Properties with Inclusion of Relativity
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
This thesis concerns quadratic response properties and their application to properties in Jablonski diagrams such as resonant two-photon absorption and excited state absorption. Our main interest lies in optical power limiting applications, and in this context, molecules containing heavy metal atoms prove superior. Therefore, we are interested in how relativity affects these properties, and in order to assess this, a four-component relativistic framework is adopted.
To properly address the molecular properties of interest, both relativistic effects and electron correlation need to be accounted for. These two properties are not additive, and, therefore, correlation needs to be incorporated into the four-component framework. We present the implementation of quadratic response properties at the four-component density functional level of theory. For second-harmonic generation, we have, with numerical examples, demonstrated that correlation and relativity are indeed not additive and that the inclusion of noncollinear magnetization is of little importance. We report that both electron correlation as well as relativity strongly affect results for second-harmonic generation. For example, relativity alone reduces the µβ-response signal by 62% and 75% for meta- and ortho-bromobenzene, respectively, and enhances the same response by 17% and 21% for meta- and ortho-iodobenzene, respectively.
In the four-component framework, we present the implementations of single and double residues of the quadratic response function, which allows for the evaluation of resonant two-photon absorption cross sections and excited state properties. Using these tools, we discuss different levels of approximation to the relativistic Hamiltonian and we demonstrate that for two-photon absorption, a proper treatment of relativistic effects qualitatively alters the spectrum. For example, already for an element as light as neon, significant differences are seen between the relativistic and nonrelativistic spectra as triplet transitions acquire substantial absorption cross sections in the former case.
Finally, quantum mechanics in conjunction with electrodynamics is applied to determine clamping levels in macroscopic samples. The microscopic properties of the optically active chromophores are determined by response theory, and then, electrodynamics is used to describe the interactions between the chromophores and incident laser pulses. Using this approach a series of molecules have been investigated and their performances have been compared and ranked in order to find novel materials for optical power limiting applications.
Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2008. , 36 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1167
relativistic quantum chemistry, molecular physics, clamping levels, four-component Hartree-Fock theory, Kohn-Sham density functional theory, response theory, nonlinear optics, second-harmonic generation, two-photon absorption, excited state properties, optical power limiting
Other Physics Topics
IdentifiersURN: urn:nbn:se:liu:diva-11035ISBN: 978-91-7393-957-7OAI: oai:DiVA.org:liu-11035DiVA: diva2:17492
2008-04-11, Planck, Hus E, Campus Valla, Linköping University, Linköping, 10:15 (English)
Vaara, Juha, Associate Professor
List of papers