arXiv subjects

José Torres-Arenas

Publications and source records attributed to José Torres-Arenas.

6 recordsLinked to original sources

arXiv2026

Structural and dynamical behavior of methane-water systems under nanoconfinement

We investigate the structural and dynamical behavior of methane water systems under nanoconfinement using molecular dynamics simulations across pore widths from 1 to 5 nm. Structural analysis reveals a strong and nonmonotonic dependence on confinement: while tetrahedral ordering partially recovers as confinement is reduced, cubic like order associated with clathrate precursors is maximized at intermediate pore sizes. Radial distribution functions show that three dimensional correlations are suppressed under strong confinement, whereas lateral ordering persists, indicating a reduction in the effective dimensionality of structural organization. Transport properties reflect the same structural competition. Parallel diffusion is nonmonotonic with pore size, while perpendicular motion is subdiffusive due to confinement induced trapping and heterogeneity. Methane exhibits stronger subdiffusion and remains dynamically coupled to the water matrix. A characteristic confinement length scale emerges at which structural ordering, dynamical heterogeneity, and solvent solute decoupling are simultaneously maximized. At strong confinement, three dimensional correlations are suppressed, leading to dimensional reduction, frustrated ordering, and inhibited nucleation.

cond-mat.soft↗

arXiv2026

Scalar curvature density as a new invariant in thermodynamic geometry: metric dependence and critical exponents

We compare two Ruppeiner metrics constructed under fixed volume and fixed particle number conditions ($g_{_V}$ and $g_{_V}$) by analyzing the scalar curvature $R$ and introducing the scalar curvature density $\mathcal{R} = \sqrt{|g|}\,R$ as a complementary geometric invariant. Three fluid models of increasing physical realism are considered: van der Waals, Lennard-Jones, and argon described by a multiparameter equation of state that correctly reproduces non-mean-field critical behavior consistent with the Ising universality class. We find that $R$ and $\mathcal{R}$ exhibit distinct critical scaling: $R \sim t^{-dν}$ is governed by the correlation length exponent, whereas $\mathcal{R} \sim t^{-(1+β)}$ scales solely with the order parameter exponent $β$, a result that follows analytically from hyperscaling and the Rushbrooke relation independently of the universality class. The $N$-metric consistently outperforms the $V$-metric in reconstructing the vapor-liquid coexistence curve away from criticality, and the four Widom lines defined by the minima of $R_{_V}$, $R_{_N}$, $\mathcal{R}_{_V}$, and $\mathcal{R}_{_N}$ display a characteristic fourfold structure reproduced across all three models. The loci where both representations yield identical geometric descriptions define two new objects: the Curvature Equality Curve (CEC, $R_{_V} = R_{_N}$) and the Curvature-Density Equality Curve (CDEC, $\mathcal{R}_{_V} = \mathcal{R}_{_N}$), with the CDEC enclosing a substantially larger region of the phase diagram in all cases. These results establish $\mathcal{R}$ as a meaningful complement to $R$ in thermodynamic geometry and highlight the nontrivial role of metric choice in the description of phase transitions and supercritical behavior.

cond-mat.stat-mech↗

arXiv2026

Thermodynamic Geometry of two-dimensional square-well fluids

Thermodynamic geometry of two-dimensional fluids has been investigated using a square-well model as a prototype fluid. A comparison with the three-dimensional case is performed in the subcritical and supercritical domains of thermodynamic space. In the subcritical region, it is found that the R-crossing method has a narrower range of validity for two-dimensional fluids compared to three-dimensional ones. On the other hand, in the supercritical region, an analysis of different Widom lines, including the R Widom line, shows that for two-dimensional fluids these lines extend further into the supercritical region than their three-dimensional counterparts. A similar behavior is observed for the validity of the Clausius--Clapeyron equation in two-dimensional fluids.

cond-mat.stat-mech↗

arXiv2026

The quantum square-well fluid: a thermodynamic geometric view

We investigate several aspects of the thermodynamic geometry for a quantum fluid with square-well interactions using a third-order perturbation theory framework based on the path-integral-necklace analogy. A comparison is made between the thermodynamic and geometric properties of the quantum fluid and its classical counterpart for the interaction ranges $λ^{*}= 1.3$, 1.5, and 1.7. In particular, we analyze the scalar curvature behavior, criticality, and the corresponding Widom lines derived from curvature and several thermodynamic response functions. Quantum effects are shown to smooth supercritical anomalies of the scalar curvature and to shift its extrema for short-range interactions, while leaving the critical exponents of both the curvature and its heat capacity consistent with mean-field predictions. Widom lines associated with temperature-dependent response functions and with the curvature scalar exhibit pronounced classical-quantum differences for short interaction ranges; in contrast, those derived from the isothermal compressibility exhibit only minor variations. Overall, these results highlight the sensitivity of geometric information of thermodynamic systems due to quantum effects and the crucial role of the interaction range in shaping supercritical thermodynamic behavior.

cond-mat.stat-mech↗

arXiv2024

Quantum Fluids in Thermodynamic Geometry

In this work, the Thermodynamic Geometry (TG) of quantum fluids (QF) is analyzed. We present results for two models. The first one is a quantum hard-sphere fluid (QHS) whose Helmholtz free energy is obtained from Path Integrals Monte Carlo simulations (PIMC). It is found that due to quantum contributions in the thermodynamic potential, the anomaly found in TG for the classical hard-sphere fluid related to the sign of the scalar curvature, is now avoided in a considerable region of the thermodynamic space. The second model is a semi-classical square-well fluid (QSW), described by a quantum hard-sphere repulsive interaction coupled with a classical attractive square-well contribution. Behavior of the semi-classical curvature scalar as a function of the thermal de Broglie wavelength $λ_B$ is analyzed for several attractive-potential ranges, and description of the semi-classical R-Widom lines defined by the maxima of the curvature scalar, are also obtained and compared with classical results for different square-well ranges.

cond-mat.stat-mech↗

arXiv2015

Microcanonical ensemble simulation method applied to discrete potential fluids

In this work we extend the applicability of the microcanonical ensemble simulation method, originally proposed to study the Ising model (A. Hüller and M. Pleimling, Int. Journal of Modern Physics C, 13, 947 (2002), arxiv:cond-mat/0110090), to the case of simple fluids. An algorithm is developed by measuring the transition rates probabilities between macroscopic states, that has as advantage with respect to conventional Monte Carlo NVT (MC-NVT) simulations that a continuous range of temperatures are covered in a single run. For a given density, this new algorithm provides the inverse temperature, that can be parametrized as a function of the internal energy, and the isochoric heat capacity is then evaluated through a numerical derivative. As an illustrative example we consider a fluid composed of particles interacting via a square-well (SW) pair potential of variable range. Equilibrium internal energies and isochoric heat capacities are obtained with very high accuracy compared with data obtained from MC-NVT simulations. These results are important in the context of the application of Hüller-Pleimling method to discrete-potential systems, that are based on a generalization of the SW and Square-Shoulder fluids properties.

cond-mat.stat-mech↗