Ab initio simulations for thermophysical properties of molecular HCNO mixtures

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We will calculate thermodynamic and transport properties of various HCNO compounds under extreme conditions of pressure and temperature typical for the interior of Neptune-like planets. Similar as in subprojects 1 and 2, we will employ state-of-the-art ab initio methods from many-particle physics that are based on density functional theory and molecular dynamics. A primary goal is the generation of equations of state for water, ammonia, methane, and their mixtures. This includes the analytic parametrization of the thermodynamic data in terms of thermodynamic potentials and the calculation of the entropy. The occurrence of dissociation and ionization processes in the fluid as well as the formation of solid and superionic phases will be investigated. The equations of state calculated here will be directly employed in the modeling of planetary interiors, which is performed in other subprojects. Our results will also be compared with the experimental findings from subproject 9.Moreover, we will calculate the diffusion coefficients, viscosities, and thermal conductivities of the HCNO mixtures. Especially hydrogen-rich stoichiometries that represent the chemical composition in thermal boundary layers in the planet at the GPa pressure range will be investigated. The ab initio methods employed here allow for a systematic investigation and characterization of such transport processes in partially dissociated and ionized matter. The results will be used in the development of novel evolution and layer formation models for Neptune-like planets in subproject 5.