Dresden 2003 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

DY: Dynamik und Statistische Physik

DY 37: Critical phenomena and phase transitions II

DY 37.4: Vortrag

Mittwoch, 26. März 2003, 17:15–17:30, G\"OR/229

Static properties of axially symmetric particles on a cubic lattice — •Michael Ricker and Rolf Schilling — Institut für Physik, Universität Mainz, Staudinger Weg 7, 55099 Mainz

Static properties of axially symmetric particles fixed on a cubic lattice are investigated. Quantities of particular interest are the static structure factors of the tensorial density fluctuations, i.e. S_{λ λ′} (q^→) = 4π/N < δ ρ_λ^∗(q^→) δ ρ_λ′(q^→)>, which can be determined by Monte Carlo (MC) simulations. Additionally, as an analytical approach, we have generalized the well-known Ornstein-Zernicke equation to lattice systems and iteratively solved it by use of the Percus-Yevick approximation. Our model consists of hard ellipsoids of revolution on a simple cubic lattice. The MC results exhibit a phase boundary in the diagram of pairs (a,b) of ellipsoid half axes, beyond which the system is in an ordered, oriented phase. Within the error margins, the corresponding correlators G_{λ λ′} (x^→) in real space decay exponentially in the disordered phase. For aspect ratios X with 0.5 < X < 2, the disordered system exhibits prominent oscillations, which can be explained by a characteristic local ordering of the ellipsoids. The Percus-Yevick theory yields very good agreement with the MC results at low enough packing fractions, and underestimates the correlations for higher densities. It also provides exponentially decaying correlations in real space, and, surprisingly, it reproduces the oscillations for X with 0.5 < X < 2 qualitatively correct.