arXiv subjects

Jose A. Cuesta

Publications and source records attributed to Jose A. Cuesta.

41 records · Page 3Linked to original sources

arXiv1998

Phase behaviour of additive binary mixtures in the limit of infinite asymmetry

We provide an exact mapping between the density functional of a binary mixture and that of the effective one-component fluid in the limit of infinite asymmetry. The fluid of parallel hard cubes is thus mapped onto that of parallel adhesive hard cubes. Its phase behaviour reveals that demixing of a very asymmetric mixture can only occur between a solvent-rich fluid and a permeated large particle solid or between two large particle solids with different packing fractions. Comparing with hard spheres mixtures we conclude that the phase behaviour of very asymmetric hard-particle mixtures can be determined from that of the large component interacting via an adhesive-like potential.

cond-mat.soft↗

arXiv1998

Demixing in a single-peak distributed polydisperse mixture of hard spheres

An analytic derivation of the spinodal of a polydisperse mixture is presented. It holds for fluids whose excess free energy can be accurately described by a function of a few moments of the size distribution. It is shown that one such mixture of hard spheres in the Percus-Yevick approximation never demixes, despite its size distribution. In the Boublik-Mansoori-Carnahan-Starling-Leland approximation, though, it demixes for a sufficiently wide log-normal size distribution. The importance of this result is twofold: first, this distribution is unimodal, and yet it phase separates; and second, log-normal size distributions appear in many experimental contexts. The same phenomenon is shown to occur for the fluid of parallel hard cubes.

cond-mat.soft↗

arXiv1997

Dimensional crossover of the fundamental-measure functional for parallel hard cubes

We present a regularization of the recently proposed fundamental-measure functional for a mixture of parallel hard cubes. The regularized functional is shown to have right dimensional crossovers to any smaller dimension, thus allowing to use it to study highly inhomogeneous phases (such as the solid phase). Furthermore, it is shown how the functional of the slightly more general model of parallel hard parallelepipeds can be obtained using the zero-dimensional functional as a generating functional. The multicomponent version of the latter system is also given, and it is suggested how to reformulate it as a restricted-orientation model for liquid crystals. Finally, the method is further extended to build a functional for a mixture of parallel hard cylinders.

cond-mat.soft↗

arXiv1996

Fluid mixtures of parallel hard cubes

The direct correlation function of a fluid mixture of parallel hard cubes is obtained by using Rosenfeld's fundamental measure approximation. This approximation is thermodynamically consistent (compressibility and virial equations of state are equal) and predicts a spinodal instability of the binary mixture for large-to-small side ratio larger than roughly 10, in qualitative agreement with simulations on the lattice version of the model. In two dimensions the system never demix, also in agreement with the simulations.

cond-mat↗

arXiv1994

Self-consistent analysis of electric field effects on Si $δ$-doped GaAs

We theoretically study the subband structure of single Si $δ$-doped GaAs inserted in a quantum well and subject to an electric field applied along the growth direction. We use an efficient self-consistent procedure to solve simultaneously the Schrödinger and Poisson equations for different values of electric field and temperature. We thus find the confining potential, the subband energies and their corresponding envelope functions, the subband occupations, and the oscillator strength of intersubband transitions. Opposite to what is usually the case when dealing with the quantum-confined Stark effect in ordinary quantum wells, we observe an abrupt drop of the energy levels whenever the external field reaches a certain value. This critical value of the field is seen to depend only slightly on temperature. The rapid change in the energy levels is accompanied by the appearance of a secondary well in the confining potential and a strong decrease of the oscillator strength between the two lowest subbands. These results open the possibility to design devices for use as optical filters controlled by an applied electric field.

cond-mat↗