Dresden 2014 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 42: Friction and Lubrication
CPP 42.3: Vortrag
Donnerstag, 3. April 2014, 10:00–10:15, ZEU 114
Determining the friction coefficient of a nanometer sized colloid by molecular dynamics simulations — •Zoran Miličević1, David M. Smith2, 3, and Ana-Sunčana Smith1, 3 — 1Institut für Theoretische Physik, FAU Erlangen-Nürnberg, Erlangen, Germany — 2Computer Chemie Centrum, FAU Erlangen-Nürnberg, Erlangen, Germany — 3Institute Rudjer Bošković, Zagreb, Croatia
Estimation of the transport coefficients of colloids in liquids is still a challenging task for computer simulations. Apart from technical difficulties, the limits of the validity of the Stokes-Einstein relation have not yet been fully established. Here, we calculate the diffusion and the friction coefficients of a nanometer sized particle in water by performing extensive molecular dynamics simulations using the GROMACS software package. We first provide a protocol for defining the hydrodynamic radius of the particle. We then show that both the diffusion and the friction coefficient, and hence the water shear viscosity, can be calculated independently. This is used to demonstrate the validity of the Stokes-Einstein relation in this regime. We compare the obtained results to the shear viscosity calculated independently from pure water simulations and the Green-Kubo relation. We investigate various approaches and present an analysis of simulation conditions required for accurate predictions of transport coefficients, with a particular emphasis on the mass and the size of the spherical particle, as well as the size of the system. As an interesting extension, we study the transport properties of a particle in water subject to a constant electric field, which breaks the otherwise isotropic nature of the system.