8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P5.6Wed 711:10-14:00Test particle theory for the van Hove distribution functionfor Brownian hard spheresAndrew Archer, 1 Paul Hopkins, 2 Andrea Fortini, 2 and Matthias Schmidt 31 Loughborough University, Loughborough, LE11 3TU, Leicestershire, United Kingdom2 University of Bristol, Bristol, United Kingdom3 Universität Bayreuth, Bayreuth, GermanyWe describe a recently developed [1, 2] test particle approach based on dynamical densityfunctional theory (DDFT) for studying the correlated time evolution of particles in a fluid. Ourtheory provides a means of calculating the van Hove distribution function by treating its self anddistinct parts as the two components of a binary fluid mixture, with the ”self” component havingonly one particle, the ”distinct” component consisting of all the other particles, and using DDFT tocalculate the time evolution of the density profiles for the two components. We apply this approachto a bulk fluid of Brownian hard spheres and compare to results for the van Hove function and theintermediate scattering function from Brownian dynamics computer simulations. We find goodagreement at low and intermediate densities using the very simple Ramakrishnan-Yussouff [3]approximation for the excess free energy functional. Since the DDFT is based on the equilibriumHelmholtz free energy functional, we can probe a free energy landscape that underlies thedynamics. Within the mean-field approximation we find that as the particle density increases, thislandscape develops a minimum, while an exact treatment of a model confined situation shows thatfor an ergodic fluid this landscape should be monotonic. We discuss possible implications forslow, glassy, and arrested dynamics at high densities. Our approach may also be applied to studythe dynamics of inhomogeneous fluids and we present results for strongly confined Brownianspheres.[1] A. J. Archer, P. Hopkins and M. Schmidt, Phys. Rev. E 75, 040501 (2007).[2] P. Hopkins, A. Fortini, A. J. Archer, M. Schmidt, J. Chem. Phys. 133, 224505 (2010).[3] T. V. Ramakrishnan and M. Yussouff, Phys. Rev. B 19, 2775 (1979).6