A simple sticking probability model is used for deducing a kernel capable to describe the kinetics of computer-simulated irreversible aggregation processes. Not only the diffusion-and reaction-limited aggregation regimes were fitted but also the whole transition region. The deduced kernel establishes λ = 0 for the entire range of sticking probabilities and helps to understand how irreversible cluster-cluster aggregation works.
In this work the well-known Frenkel-Mulder phase diagram of hard ellipsoids of revolution [Mol. Phys. 55, 1171] is revisited by means of replica exchange Monte Carlo simulations. The method provides good sampling of dense systems and so, solid phases can be accessed without the need of imposing a given structure. At high densities, we found plastic solids and fcc-like crystals for semi-spherical ellipsoids (prolates and oblates), and SM2 structures [Phys. Rev. E 75, 020402 (2007)] for x : 1-prolates and 1 : x-oblates with x≥3. The revised fluid-crystal and isotropic-nematic transitions reasonably agree with those presented in the Frenkel-Mulder diagram. An interesting result is that, for small system sizes (100 particles), we obtained 2:1 and 1.5:1-prolate equations of state without transitions, while some order is developed at large densities. Furthermore, the symmetric oblate cases are also reluctant to form ordered phases.
The effective interaction between a sphere with an open cavity (lock) and a spherical macroparticle (key), both immersed in a hard sphere fluid, is studied by means of Monte Carlo simulations. As a result, a 2d map of the key-lock effective interaction potential is constructed, which leads to the proposal of a self-assembling mechanism: there exists trajectories through which the key-lock pair could assemble avoiding trespassing potential barriers. Hence, solely the entropic contribution can induce their self-assembling even in the absence of attractive forces. This study points out the solvent contribution within the underlying mechanisms of substrate-protein assembly/disassembly processes, which are important steps of the enzyme catalysis and protein mediated transport.
Colloidal suspensions of Laponite clay platelets are studied by means of Brownian dynamics simulations. The platelets carry discrete charged sites which interact via a Yukawa potential. As in the paper by S. Kutter et al. [J. Chem. Phys. 112, 311 (2000)], two models are considered. In the first one all surface sites are identically negative charged, whereas in the second one, rim charges of opposite sign are included. These models mimic the behavior of the Laponite particles in different media. They are employed in a series of simulations for different Laponite concentrations and for two values of the Debye length. For the equilibrium states, the system structure is studied by center-to-center and orientational pair distribution functions. Long-time translational and rotational self-diffusion coefficients are computed by two different methods, which yield very similar results.
We report the phase diagram of two-dimensional hard ellipses as obtained from replica exchange Monte Carlo simulations. The replica exchange is implemented by expanding the isobaric ensemble in pressure. The phase diagram shows four regions: isotropic, nematic, plastic, and solid (letting aside the hexatic phase at the isotropic-plastic two-step transition [PRL 107, 155704 (2011)]). At low anisotropies, the isotropic fluid turns into a plastic phase which in turn yields a solid for increasing pressure (area fraction). Intermediate anisotropies lead to a single first order transition (isotropic-solid). Finally, large anisotropies yield an isotropic-nematic transition at low pressures and a high-pressure nematic-solid transition. We obtain continuous isotropic-nematic transitions. For the transitions involving quasi-long-range positional ordering, i. e. isotropic-plastic, isotropic-solid, and nematic-solid, we observe bimodal probability density functions. This supports first order transition scenarios.
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