The thermodynamic description of molecular systems composed of water, ammonia, and methane at high pressure up to 1 TPa is the subject of this thesis. The focus lies on the calculation of equations of state, phase diagrams, and their characterization by employing the quantum-statistical method density functional theory molecular dynamics. In particular superionic phases are investigated using evolutionary structure searching and the linear mixing approximation is validated. The obtained simulation results serve as input for modeling the interior structure of giant planets such as Uranus.<eng>
