G. Navascués

Phase diagrams of systems of particles interacting via repulsive potentials

We use a recently developed density-functional perturbation theory, which has been applied successfully to predict phase diagrams of systems of attractive particles, to describe the phase diagram of particles interacting via repulsive potentials. We consider potentials composed of a hard-sphere core plus a repulsive term. Specifically, we have investigated square shoulder and repulsive Yukawa terms. We show that, when the range of the interaction is very short, the shoulder potential leads to solid–solid coexistence involving two face-centered cubic structures, in analogy to an attractive square-well potential. Comparison with simulation results shows that the theory is quantitatively correct. If the range of the potentials is sufficiently long, we also find that a body-centered cubic structure can be stabilized. By considering the phase behavior at zero temperature, we argue that several triple points, involving coexistence of fluid and/or solid phases, may occur. A repulsive Yukawa term also shows a reg...

Theoretical approach to the correlations of a classical crystal

We present the first theoretical approach to the angular-average of the two-body correlation function

Solid-solid transitions induced by repulsive interactions

\tilde g(r)

Solid‐to‐solid isostructural transition in the hard sphere/attractive Yukawa system

for simple solids. It is based on three sum rules for

EQUATION OF STATE OF THE HARD-SPHERE CRYSTAL

\tilde g(r)

THERMODYNAMIC CONSISTENCY OF THE HARD-SPHERE SOLID DISTRIBUTION FUNCTION

: the compressibility and virial equations and the normalization. We apply the theory to determine this correlation function for the case of the FCC solid phase of hard spheres. The agreement with simulation data is excellent over all the density range. The application to other simple systems is discussed. The approach opens a new route to perturbation theories for simple solids.

Phase diagram of a square-well model in two dimensions

We show that a rich variety of crystalline structures, and a corresponding diversity of the associated phase diagrams, result from the presence in the pair potential of a soft repulsion in addition to a hard core. We use different forms for the soft repulsion, and show that the results are sensitive to the details of the potentials (in particular, their convexity) even if the range of the soft repulsion is limited to a small fraction of the hard-core diameter. Our demonstration combines exact ground-state analysis with first-order perturbation theory at finite temperatures. The relevance of our work to certain features found in real systems is also discussed.

Self-consistent nonperturbative theory: Treatment of colloidal-type interactions

A thermodynamically consistent density functional-perturbation theory is used to study the isostructural solid-to-solid transition which takes place in the hard sphere/attractive Yukawa system when the Yukawa tail is sufficiently short-ranged. A comparison with results for the square well potential allows us to study the effect of the attractive potential form on the solid-solid transition. Reasonable agreement with simulations is found for the main transition properties as well as for the phase diagram evolution with the the range of the attractive potential.A thermodynamically consistent density functional‐perturbation theory is used to study the isostructural solid‐to‐solid transition which takes place in the hard sphere/attractive Yukawa system when the Yukawa tail is sufficiently short ranged. A comparison with results for the square well potential allows us to study the effect of the attractive potential form on the solid–solid transition. Reasonable agreement with simulations is found for the main transition properties as well as for the phase diagram evolution with the range of the attractive potential.

Free-energy correction due to center-of-mass constraint in crystals

A new approach to the averaged two-particle distribution function of a crystalline phase is presented. It includes an indirect check of the merit of the Gaussian approximation for the local density and a new way to inferring values of the thermodynamic variables from simulation data. The equation of state and the compressibility of the hard-sphere FCC crystal is computed from Tarazona free energy density functional [Phys. Rev. A {\bf 31}, 2672 (1985)]. They are in excellent agreement with simulation results over the physical range of densities up to almost close packing. We also include the comparison with the results obtained by two other functional approaches which are also excellent.

Self-consistent nonperturbative theory: Application to a two-dimensional square-well system

A discussion about the role of the two‐particle density function in the fundamental equation of the compressibility is presented. The thermodynamic inconsistency found by different authors between the compressibility obtained from the equation of state and that from the compressibility equation, in both cases using simulation data, is clarified. A new parameterization for the solid radial distribution function, which includes properly the compressibility effects, is proposed.