PROJECTS

Local ab initio schemes to describe excitations in polymers and solids

PRINCIPAL INVESTIGATOR

Prof. Dr. Martin Albrecht Universität Siegen Theoretische Chemie 57068 Siegen Germany 0271/ 7404217 0271/ 7402555 m.albrecht@uni-siegen.de

PROJECT RESEARCH ASSISTANT

ABSTRACT

A profound theoretical understanding and description of excited states in solids and polymers is of paramount interest in current research. Sophisticated experiments allow to probe more and more complex quasiparticles representing excited states, like excitons or biexcitons. However, an ab initio treatment of excited states in extended periodic systems has remained an important challenge up to the present. Various demands like full applicability to excited states, systematical improvablility and size-consistency have to be satisfied by a multi reference method. Finally the unfavourable scaling of numerical effort has to be overcome.For quite some time considerable effort was spent on the description of the simplest quasiparticles and their energy levels, i. e. the band structure. The applicant has made contributions of his own with the development, implementation and application of different methods. At present the focus is shifting to the next more involved problem, that of excitons. While investigations for polymers and solids are possible within the frame of certain schemes, these methods lack some features desirable for ab initio tools. On the other hand wave function based methods, which meet such requirements, have been applied basically to small molecules. The project suggested strives to make an effort towards bridging this gap. Wave function based approaches are to be formulated and implemented so as to bring polymers and solids well into their scope of application as part of the first two years of the PhD project (for which funding has already been granted). Specifically this project application for the third year will focus on specific problems of infinite lattice summations in one- and three-dimensional structures which appear on top of general considerations of an abstract CI space. In addition, a feasible program package is to be developed, which will allow for first realistic applications such as polyacetylene and LiH. These activities will be based on and supported by recently developed theoretical considerations and program packages provided by the group of the applicant as well as the previous work of the first two years of the overall PhD project to be realized by the candidate. In fact the project can be seen as a consequent and logical evolvement of the investigations conducted up to the present, while at the same time it contributes to an exciting and very active new field of research. In sum a solid theoretical background and helpful experience is available to realize the project. Collaborations with other groups provide additional supportive background. A state-of-the-art computer park which has been enlarged regularly guarantees the necessary computational frame.