Winfried Lorenzen

• Dr. rer. nat.
• Bundesnetzagentur

We used molecular dynamics simulations based on density functional theory to study the thermophysical properties of warm dense helium. The influence of different exchange-correlation (XC) functionals was analyzed. We calculated the equation of state at high pressures up to several Mbar and temperatures up to 100 000 K in order to reconstruct recent...

The description of the interior structure and evolution of the Solar System giant planets continues to be a serious challenge. The most prominent example is Saturn for which simple homogeneous evolution models yield ages between 2 and 3 billion years (Gyr), i.e. much shorter than the age of the Solar System of Gyr. It has long been suggested that H...

We present new equations of state (EOS) for hydrogen and helium covering a wide range of temperatures from 60 K to 10$^7$ K and densities from $10^{-10}$ g/cm$^3$ to $10^3$ g/cm$^3$. They include an extended set of ab initio EOS data for the strongly correlated quantum regime with an accurate connection to data derived from other approaches for the...

We give an introduction into the method of quantum molecular dynamics simulations which combines density functional theory with classical molecular dynamics. This method has demonstrated its predictive power in determining the thermophysical properties of matter under extreme conditions as found, e.g., in astrophysical objects like giant planets an...

Abstract A scientific forum on "The Future Science of Exoplanets and Their Systems," sponsored by Europlanet (*) and the International Space Science Institute (ISSI) (†) and co-organized by the Center for Space and Habitability (CSH) (‡) of the University of Bern, was held during December 5 and 6, 2012, in Bern, Switzerland. It gathered 24 well-kno...

We determine basic thermodynamic and transport properties of hydrogen-helium-water mixtures for the extreme conditions along Jupiter's adiabat via ab initio simulations, which are compiled in an accurate and consistent data set. In particular, we calculate the electrical and thermal conductivity, the shear and longitudinal viscosity, and diffusion...

The planet Jupiter contains matter under extreme pressures in the megabar regime and temperatures of several thousand Kelvin. Accurate knowledge about the behavior of the major constituents, hydrogen and helium, is required to model and understand the interior of Jupiter and other gas giant planets. In particular, transport properties like the ther...

Hydrogen-helium mixtures have long been predicted to undergo demixing at high pressures of several megabars which occur in the interiors of giant planets such as Jupiter and Saturn. This effect is most important to understand their evolution and current interior structure. Ab initio calculations have already proven their potential to give precise p...

We use ab initio molecular-dynamics simulations to study the nonmetal-to-metal transition in dense liquid hydrogen. By calculating the equation of state of hydrogen at high pressures up to several megabars and temperatures above the melting line up to 1500 K we confirm the first-order nature of this transition at these temperatures. We characterize...

We present new results in modeling the interiors of Giant Planets (GP) and Brown Dwarfs (BD). In general models of the interior rely on equation of state data for planetary materials which have considerable uncertainties in the high-pressure domain. Our calculations are based on ab initio equation of state (EOS) data for hydrogen, helium, hydrogen-...

We present new results for the interior of solar as well as extrasolar giant planets based on ab initio molecular dynamics simulations for the most abundant planetary materials hydrogen, helium, and water. The equation of state, the electrical conductivity and reflectivity can be calculated up to high pressures; very good agreement with shock‐wav...

We have performed quantum molecular dynamics simulations based on finite-temperature density functional theory for warm dense hydrogen-helium mixtures for conditions relevant for the interior of giant planets. We derive the miscibility gap from the EOS data and discuss the consequences for the interior structure of Jupiter and Saturn. Calculations...

We have performed quantum molecular dynamics simulations using finite-temperature density functional theory (FT-DFT-MD) to calculate accurate equation of state data for the most abundant materials in giant planets hydrogen, helium, and water in the warm dense matter region. We discuss the phase diagram of water up to ultra-high pressures and identi...

We present results of ab initio finite-temperature density functional theory molecular dynamics simulations for fluid hydrogen-helium mixtures at megabar pressures. The location of the miscibility gap is derived from the equation of state data. We find a close relation between hydrogen-helium phase separation and the continuous nonmetal-to-metal tr...

Giant planets such as Jupiter and Saturn in our solar system have attracted a renewed lively interest since the discovery of extrasolar planets. The study of planetary formation processes, of the internal structure and evolution of giant planets are challenging problems in this context. Furthermore, the interior of giant planets is a perfect labora...