PROJECTS

Optimization of Fragment Electron Densities for the Usage in Mixed Quantum Mechanical / Molecular Mechanical (QM/MM) and Fragment-Based Quantum Mechanical Methods

PRINCIPAL INVESTIGATOR

Prof. Dr.-Ing. Thomas Eckart Exner Universität Koblenz Fachbereich Chemie +49 7531 882015 +49 7531 883587 thomas.exner@uni-konstanz.de

PROJECT RESEARCH ASSISTANT

ABSTRACT

Based on the adjustable density matrix assembler (ADMA) method, a platform for the quantitative testing of fragment-based approximations of electron densities will be developed. Such fragment electron densities are used, on the one hand, in fragment-based approaches, in which independent quantum mechanical calculations are performed for these fragments, and, on the other hand, in mixed QM/MM methods. For a correct description, these fragments should represent the corresponding parts of the total system as good as possible. To achieve this, a number of techniques, e.g. the inclusion of additional parts in the quantum mechanical calculations of the fragments, the usage of partial charges to represent even larger surroundings, and the optimization of the border regions, have been introduced. These techniques will be adapted for the ADMA method and their performance will be compared with a number of test examples. An advantage of the ADMA method concerning this comparison is that the optimal solution is available in the form of the direct quantum mechanical calculation of the total system. QM/MM methods are parameterized on small systems and the parameters are then transferred to the large system under investigation. In the ADMA method, the parameterization can be done directly using the large system and the quality of the approximation can be judged by the comparison of the density matrices and total energies. In this way, the optimal approximation method and the optimal parameters for this method will be obtained, which can then also be used in other fragment-based QM or QM/MM methods.