Modeling Molecular Properties of Interest for Streamer Studies
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- Institutt for kjemi 
If an insulating material is stressed by sufficiently large electric field, a plasma channel may be created which destroys the materials insulating properties. The processes involved are complicated and the field of research pushes into the boundaries of the unknown. Attempting to understand the processes involved from a fundamental point of view reveals many problems, and maybe that is what makes this field so interesting. Two of the properties of interest which can be calculated from standard quantum chemical methods is the polarizability and the ionization potential. Therefore it is these two properties which have been studied further. The molecules first order response to an electric field is given by the polarizability, and thus is an important property when a material is stressed by an electric field. In addition, the interaction between a charged and a neutral molecule is given by the polarizability. In the two first works (paper 1 and 2) a model based on atomic parameters for the polarizability is given. The third work (paper 3) is an attempt to link the polarizability model to a force field which is capable of simulating a plasma phase, which contains both neutral and charged particles. Ionization potential is the energy required to ionize a neutral system, and is the most important molecular descriptor for all ionization mechanisms. In paper 4 we use standard quantum mechanical software to calculate the ionization potential and results in good agreement to experimental values are obtained. It is realized that there are a lot of other interesting molecular properties which also could have been studied, but many of these are difficult to calculate. A discussion regarding some of these properties are given in paper 4. In paper 5 the ionization potential and ionization mechanism are studied in greater detail. Speci cally it is found that the ionization potential of a molecule change in an electric eld, and that the reduction in ionization potential due to the eld cannot be ignored when studying high-field phenomena.