Abstract
We investigate, via Monte Carlo simulations, the relation between thermodynamic and dynamic properties
of an associating lattice gas (ALG) model, in which particles interact through a soft core potential (van der Waals) and
orientational degrees of freedom (ice-like interactions).
In two dimensions the particles are in a triangular lattice and the competition between directional
attractive forces and the repulsive soft core results in two liquid phases, double criticality and density anomaly.
The diffusion coefficient, D, is obtained as a function of density
at fixed temperature. At high densities D has a maximum at $\rho_D_max$ and at low densities, it has a minimum at $\rho_D_min$. In the region, $\rho_D_min<\rho<\rho_D_max$, the behavior of the diffusion coefficient with density differs from that of a normal liquids: the diffusion coefficient increases with density.
By calculating the pressure of the extrema in diffusivity, we show that in the pressure-temperature phase diagram, the line of extrema in diffusivity is close to the liquid-liquid critical point an lies inside the temperature of maximum density (TMD).
In three dimensions the particles are arranged in a body centered cubic lattice and the same scenario appears: two liquid phases, two critical points and density anomaly.
In this case, the behavior of the diffusion coefficient with density is also anomalous.
The pressure-temperature phase diagram shows that diffusion extrema line has a shift in relation of
the two dimension model, but again is close to the liquid-liquid critical point and TMD.
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