Regensburg 2013 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 19: Poster: Crystallization, Nucleation and Self Assembly

CPP 19.6: Poster

Dienstag, 12. März 2013, 18:15–20:15, Poster C

Free energies of fcc, hcp, and bcc phases of hard sphere crystals — •Mohammad Hossein Yamani and Martin Oettel — Institut für Angewandte Physik, Universität Tübingen, Germany

We use density functional theory of fundamental measure type (FMT) to evaluate the fully unconstrained minimized periodic fcc, hcp and bcc crystal profiles. Previous FMT results in the case of fcc compare very well to simulation results [1]. hcp and fcc differ only in the stacking sequence of hexagonally packed planes of particles, and thus one expects only a small free-energy difference between these two structures. FMT predicts hcp to be more stable than fcc by a free energy difference per particle of the order of 0.001 k_B T. Instead, simulation results show that fcc is more stable than hcp by about the same free energy difference. We rationalize these findings using Stillinger’s expansion [2] for the crystal partition function in the number n of correlated, free particles in a matrix of frozen particles at ideal lattice positions. It turns out that the stability of hcp over fcc holds for a truncation at n=2, giving approximately the same hcp-fcc free energy difference as FMT. For a reversal of stability truncation at higher n is required.
M. Oettel et al., Phys. Rev. E 82, 051404 (2010).
W. G. Rudd et al., J. Chem. Phys. 49, 4857 (1968).