Advanced Modelling of He Droplets

In course of the "Erwin-Schrödinger fellowship abroad" I attend to develop a force field to describe the interaction of helium atoms with solvents. This theoretical investigation is based on helium droplets experiments carried out in Innsbruck, and the obtained results will be constantly proved by experimental results. We use therefore measurements on small systems, which have been already carried out; however if it is necessary experimental data is required, the measurements are going to be carried out in Innsbruck. The theoretical work at Uppsala University in Sweden for 20 months under supervision of Prof. Kersti Hermansson will be divided in four steps and altogether these steps will allow me to model molecules and ions solvated by Helium atoms. In the first part of the project, the interaction of helium atoms with small neutral, cationic and anionic atomic and molecular systems (e.g. Chloride ion, chloroform and water) will be studied using quantum mechanical electronic structure (ab initio) calculations tested by different levels of theory and basis sets. This is important to determine the right level and basis set to describe the weak interaction of Helium atoms with molecules. The chosen level of theory/basis sets will be used in the second step of the project in the calculation of many potential energy surfaces (PES) corresponding to a large number of different coordination geometries for each molecule - Helium system. The third step will be the derivation of an advanced state-of-the-art "many-body force-field" for the He-solvated molecules. A force-field has a simplified analytical functional form compared to the iterative electronic structure calculations and therefore a much reduced computational cost. The functional form and parameter set necessary to describe the many-body PES will be derived for each solvated molecule/ion. In the fourth step the functions fitted in step 3 will be used in molecular dynamics (MD) simulations of the solvation of the molecules in small liquid Helium droplets (containing some 10-100 helium atoms. After the successful implementation of the developed force field, the work shall be continued in Innsbruck within the return phase of 12 months. Experiments with even larger systems will prove the quality of our force field approach and the validity of its results. The constant exchange between the experimental group in Innsbruck and the theoretical group in Sweden shall be the key to a successful accomplishment of the project.