(Dr. rer. nat. Robert Hellmann)
Thermophysical properties of fluids can today be determined very accurately from first principles (ab initio). A prerequisite for such calculations are pair potentials, which describe the interaction energy between two molecules as a function of their separation and mutual orientation. For calculations on dense gases and liquids, so-called nonadditive three-body potentials are additionally required. In our work group, interaction energies are computed by means of the supermolecular approach using standard quantum-chemical program packages such as CFOUR or ORCA. Such calculation have to be performed for a large number of interparticle separations and mutual orientations in order to obtain a complete description of the intermolecular interaction.
In the next step, suitable mathematical functions are fitted to the calculated interaction energies. Using these potential functions, one can, for example, calculate the second, third, and higher virial coefficients employing statistical thermodynamics. Transport properties in low-density gases and gas mixtures are accessible from the pair potentials using the kinetic theory of gases, with the respective computer codes developed in our work group being unique. In future work, we intend to perform also molecular dynamics and Monte Carlo simulations. Today, empirical potential functions are still widely used in such simulations, which severely limits the achievable accuracy.
Whenever possible, the calculated property values are compared with experimental data from our own group or from the literature in order to enable a mutual validation of theory and experiment. A great advantage of first-principles approaches over experiments is that a high accuracy can also be achieved at very low or very high temperatures and for toxic, corrosive, and explosive fluids and fluid mixtures. The experimental effort is often unjustifiably high in these cases.
The work group operates a number of powerful computing servers for the first-principles calculations. In addition, the university’s high performance computing facilities are used for parts of the calculations.
Letzte Änderung: 25. May 2022