Szortyka Marcia M, Henriques Vera B, Girardi Mauricio, Barbosa Marcia C
Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, Porto Alegre, Rio Grande do Sul 91501-970, Brazil.
J Chem Phys. 2009 May 14;130(18):184902. doi: 10.1063/1.3129842.
Using Monte Carlo simulations we investigate some new aspects of the phase diagram and the behavior of the diffusion coefficient in an associating lattice gas (ALG) model on different regions of the phase diagram. The ALG model combines a two dimensional lattice gas where particles interact through a soft core potential and orientational degrees of freedom. The competition between soft core potential and directional attractive forces results in a high density liquid phase, a low density liquid phase, and a gas phase. Besides anomalies in the behavior of the density with the temperature at constant pressure and of the diffusion coefficient with density at constant temperature are also found. The two liquid phases are separated by a coexistence line that ends in a bicritical point. The low density liquid phase is separated from the gas phase by a coexistence line that ends in tricritical point. The bicritical and tricritical points are linked by a critical lambda-line. The high density liquid phase and the fluid phases are separated by a second critical tau-line. We then investigate how the diffusion coefficient behaves on different regions of the chemical potential-temperature phase diagram. We find that diffusivity undergoes two types of dynamic transitions: a fragile-to-strong transition when the critical lambda-line is crossed by decreasing the temperature at a constant chemical potential; and a strong-to-strong transition when the critical tau-line is crossed by decreasing the temperature at a constant chemical potential.
我们使用蒙特卡罗模拟研究了相图的一些新方面，以及在相图不同区域的缔合晶格气体（ALG）模型中扩散系数的行为。ALG模型结合了一种二维晶格气体，其中粒子通过软核势和取向自由度相互作用。软核势与定向吸引力之间的竞争导致了高密度液相、低密度液相和气相。此外，还发现了在恒压下密度随温度的行为以及在恒温下扩散系数随密度的行为中的异常现象。两个液相由一条终止于双临界点的共存线分隔。低密度液相与气相由一条终止于三临界点的共存线分隔。双临界点和三临界点由一条临界λ线相连。高密度液相与流体相由第二条临界τ线分隔。然后，我们研究了扩散系数在化学势 - 温度相图的不同区域上的行为。我们发现扩散率经历了两种类型的动态转变：当在恒定化学势下通过降低温度穿过临界λ线时发生从脆弱到强烈的转变；当在恒定化学势下通过降低温度穿过临界τ线时发生从强烈到强烈的转变。
