Peter Virnau: Research

Collective behavior of self-propelled particles

Dynamical collective behavior observed in, e.g., schools of fish and flocks of birds can often be described with simple models of so-called self-propelled particles. Even complex behavior can be reproduced by simple rules that are followed by all individuals (e.g., follow your neighbors but do not bump into them). On the microscale, both bacteria and colloidal particles have emerged as model systems to study a wealth of different phenomena such as swirling, swarming, and turbulence.

We are especially interested in the novel collective properties of colloidal Janus particles that are propelled by diffusio-phoresis or similar means, which have been realized experimentally very recently. Depending on the interplay of volume exclusion, hydrodynamic alignment of orientations, and attractive forces, several phenomena like living crystals and phase separation are observed.

For more information, please contact Thomas Speck and Peter Virnau.

Simulation of Nucleation and "Critical Clusters"

Metastable phases decay by rare statistical fluctuations, termed "nucleation", where a "critical cluster" (i.e., a nanoscopic aggregate of the new phase having the minimal size to be able to grow) forms. Such critical clusters may form in the bulk ("homogeneous nucleation"), which facilitate this cluster formation by reducing the free energy barrier that needs to be overcome. Specialized computer simulation methods are developed to estimate the surface excess free energies, that control these processes, and related quantities (such as contact angles, line tension, Tolman length). This research is carried out in collaboration with S. K. Das (Bangalore), S. Egorov (University of Virginia) and A. Tröster (Vienna Technical University). For more information, please contact Kurt Binder and/or Peter Virnau.

Knots in polymers, proteins and DNA


Although globular homopolymers are typically highly knotted, less than one in a hundred protein structures contain a knot. Nevertheless, intriguing counter-examples exist, like the most complicated protein knot, which was discovered during a diploma thesis in our group (see figure on the left). Apart from analyzing biological data, we perform Monte Carlo simulations of simplified protein and DNA models to learn more about entanglements in viral DNA, proteins and chromatin. On the latter, we collaborate with an experimental biochemistry group from Cambridge University to unravel the structure of DNA in the cell nucleus. If you are interested in interdisciplinary investigations at the frontier of physics, mathematics and molecular biology, please contact Peter Virnau.