arXiv subjects

Prabal K. Maiti

Publications and source records attributed to Prabal K. Maiti.

At least 19 recordsLinked to original sources

arXiv2026

Effect of Spherical Confinement on the 2-TIPS of Soft Repulsive Spherocylinders

We studied the 2-Temperature induced phase separation (2-TIPS) in a system of soft repulsive sphe rocylinders (SRS), confined on the surface of a sphere. We used two different anchoring conditions for the SRS on the spherical surface- free and tangential. For the free anchoring, increasing either the packing fraction or the rod aspect ratio suppresses phase separation between the active and passive subsystems, and the system corresponds to a dense-dilute phase co-existence. These phenomena can be explained via the trapping effect and are emergent due to the confinement. For the tangential anchoring, the system phase separates from its initial isotropic state into a locally ordered dense region and a disordered dilute region. Our work provides useful insights into phase separation in binary mixtures under spherical confinement.

cond-mat.soft↗

arXiv2026

Memory Control of Ice Growth During Non-Equilibrium Freezing of Water

Freezing of supercooled water is a classic non-equilibrium problem, yet the influence of thermal history on crystallization remains unclear. Using molecular dynamics simulations with the TIP4P/Ice model, we investigate how the initial temperature $T_i$ shapes freezing following rapid quenching to 250 K. By monitoring the evolution of hydrogen-bonded ring structures, we find a non-monotonic dependence of the freezing time $t_F$ on $T_i$, with the slowest crystallization occurring near 300 K. Remarkably, this means that initially hotter water can freeze faster than cooler water, a molecular-scale analogue of the Mpemba effect. A non-stationary generalized Langevin equation framework shows that two-time memory kernels retain information about the system's thermal past, directly influencing crystallization dynamics. Structural analysis further reveals that five-membered rings act as kinetic traps, while correlations among ring types regulate the accessibility of ice-like motifs. These results uncover a molecular origin of memory-driven freezing and establish structural memory as a key driver of non-equilibrium phase transitions.

cond-mat.mes-hall↗

arXiv2026

Comparative Assessment of Thermal Transport Theories: Dual-Channel Mechanism Dictates Heat Transport in Ultralow-$κ$ Materials

Anomalous heat transport in strongly anharmonic crystalline solids poses both a fundamental challenge to the theoretical understanding and an opportunity for thermoelectric and thermal barrier coating applications. Although Green-Kubo theory reproduces experimental thermal conductivity ($κ$) at high temperatures, it lacks microscopic insight and neglects the Bose-Einstein statistics of lattice vibrations. On the other hand, the conventional Boltzmann transport equation (BTE) framework, based on a phonon-gas picture, fails due to strong anharmonicity-induced overdamped phonons. Herein, the thermal transport properties in TlAgSe, a metal chalcogenide, and Cs$_2$PbI$_2$C$_2$, an all-inorganic layered Ruddlesden-Popper perovskite, are investigated by explicitly accounting for temperature-dependent lattice dynamics through machine learning interatomic potentials and employing the Wigner transport equation (WTE) framework. Crucially, heat conduction is governed not only by higher-order phonon scattering-dominated populations' transport channel described within the BTE, but also by a coherences' channel in the WTE framework arising from wave-like interbranch coherence between eigenstates. Incorporating four-phonon scattering, WTE predicts average room-temperature $κ$ values of 0.31 Wm$^{-1}$K$^{-1}$ (TlAgSe) and 0.38 Wm$^{-1}$K$^{-1}$ (Cs$_2$PbI$_2$C$_2$), in excellent agreement with experiments. Phonon scattering-rate analysis reveals strong coherences' contributions and prevalent overdamped phonon modes, demonstrating the breakdown of the conventional BTE framework based on the phonon quasiparticle picture with only first-order anharmonic perturbation. This computational approach provides a unified description of heat transport in ultralow-$κ$ materials, offering a basis for the rational design of phononic and thermoelectric devices.

cond-mat.mtrl-sci↗

arXiv2026

Two-Temperature Induced Phase Separation: Non-equilibrium Phase Behavior, Ordering, and Kinetics

Two-temperature induced phase separation (2-TIPS) has emerged as a generic non-equilibrium mechanism in scalar active systems with heterogeneous activity, where particles coupled to different thermal reservoirs spontaneously demix into dense cold and dilute hot phases. Unlike equilibrium phase separation or motility-induced phase separation (MIPS), 2-TIPS is driven solely by unequal energy injection and the resulting heat flux between particle species. This review summarizes recent advances in 2-TIPS across diverse soft-matter systems, highlighting both its universal non-equilibrium mechanisms and the emergent ordered phases arising from particle shape anisotropy, chirality, confinement, and topology. We further discuss density-dependent phase-separation kinetics and coarse-grained descriptions linking microscopic dynamics to macroscopic behavior, and outline key directions for future research.

cond-mat.soft↗

arXiv2026

Density-Induced Reentrant Coarsening in a Two-Temperature System

Understanding how nonequilibrium driving modifies phase-separation kinetics remains a fundamental challenge. Here we show that phase separation in a two-temperature system exhibits a striking density-induced reentrant coarsening behavior. Using Brownian dynamics simulations and a coarse-grained field-theoretic model, we find that the characteristic domain size grows as $L(t)\sim t^{1/z}$, displaying a reentrant sequence $(t^{1/3} \rightarrow t^{1/4}\rightarrow t^{1/3})$ with increasing density. While the low- and high-density regimes are governed by classical curvature-driven bulk diffusion, the intermediate-density regime exhibits anomalously slow growth. We show that this slowdown originates from a transport bottleneck arising from the interplay of particle diffusivity, particle availability, and attachment kinetics, which suppresses the effective mass flux between domains. Unlike equilibrium phase separation, where density primarily affects morphology and crossover scales, the two-temperature drive renders density a key control parameter for coarsening pathways. Our results uncover a nonequilibrium mechanism for anomalous domain growth in two-temperature systems.

cond-mat.soft↗

arXiv2026

Ionic Liquid-Driven Modulation of DNA Brush Morphology on Nanoparticle Surfaces

The morphology of DNA is strongly influenced by its surrounding environment, including factors such as pH, salt type and valency, and the presence of polymers. Inorganic salts are known to reduce the DNA chain length through mechanisms like electrostatic screening and ion bridging. In contrast, ionic liquids, a new class of organic salts, have previously been found to increase the DNA chain length, indicating a distinct mode of interaction between the ionic liquid and DNA chains. This study utilizes self-assembled DNA-AuNPs as a model system to examine changes in the DNA chain morphology and the nanoscale interaction mechanisms in ionic liquid environment. The DNA chain lengths are measured in solution using X-ray scattering measurements at varying concentrations of two imidazolium ([BMIM] acetate and [EMIM] acetate) based ionic liquids. Additionally, Molecular Dynamics (MD) simulations are performed mimicking the experimental system. Our results suggest an interplay of electrostatic and groove-binding interactions governing the DNA chain morphology, which depends on IL concentration and the composition of the DNA chains. It has been found that for DNA chains with majority ssDNA, electrostatic interaction dominate, however with increasing composition of double strands, the DNA chains exhibits compaction due to non-electrostatic hydrophobic groove-binding mechanism.

cond-mat.soft↗

arXiv2025

Phase separation kinetics of 2-TIPS at low density: Cluster growth by ballistic agglomeration

We study the kinetics of two-temperature induced phase separation (2-TIPS) in dilute binary mixtures of active ("hot") and passive ("cold") particles using molecular dynamics simulations and a coarse-grained hydrodynamic model. Following a temperature quench, cold particles nucleate into mobile clusters that move ballistically and merge through successive coalescence events. The resulting domain growth exhibits dynamic scaling with a growth exponent of approximately 0.7, markedly faster than diffusive coarsening. We identify this regime as ballistic agglomeration of cold clusters, demonstrating a distinct nonequilibrium growth mechanism in low-density scalar active systems.

cond-mat.soft↗

arXiv2025

Phase behaviour and defect structure of soft rods on a sphere

Using particle-resolved molecular-dynamics simulations, we compute the phase diagram for soft repulsive spherocylinders confined on the surface of a sphere. While crystal (K), smectic (Sm), and isotropic (I) phases exhibit a stability region for any aspect ratio of the spherocylinders, a nematic phase emerges only beyond a critical aspect ratio lying between 6.0 and 7.0. As required by the topology of the confining sphere, the ordered phases exhibit a total orientational defect charge of +2. In detail, the crystal and smectic phases exhibit two +1 defects at the poles, whereas the nematic phase features four +1/2 defects which are connected along a great circle. For aspect ratios above the critical value, lowering the packing fraction drives a sequence of transitions: the crystal melts into a smectic phase, which then transforms into a nematic through the splitting of the +1 defects into pairs of +1/2 defects that progressively move apart, thereby increasing their angular separation. Eventually, at very low densities, orientational fluctuations stabilize an isotropic phase. Our simulations data can be experimentally verified in Pickering emulsions and are relevant to understand the morphogenesis in epithelial tissues.

cond-mat.soft↗

arXiv2025

Diffusion-entropy scaling across dimensions

A quantitative relationship between the diffusion coefficient $D$ of a tagged particle in a liquid and the entropy $S$ of that liquid has long been sought, as it would allow entropy to be inferred directly from diffusion measurements and transport properties to be predicted from thermodynamic information. Here, we employ extensive computer simulations to independently compute both $D$ and $S$ for Lennard-Jones (LJ) liquids and for water across a wide range of thermodynamic state points. Our study covers two and three dimensions for both systems, and additionally explores one-dimensional confinement for water. We find that the ratio of diffusion coefficients between two states follows an almost perfect exponential dependence on their entropy difference. For LJ liquids, the exponential prefactor exhibits a pronounced dependence on dimensionality $d$, consistent in trend but quantitatively distinct from theoretical predictions. In contrast, water shows a strikingly weak dimensionality $d$ dependence, deviating from theory, which we attribute to the dominant role of jump diffusion. Remarkably, the exponential diffusion-entropy relationship persists even when translational and rotational contributions to entropy are separated and considered individually. This robustness suggests that entropy provides a unifying measure governing particle mobility in liquids, largely independent of microscopic mechanisms or dimensional constraints.

cond-mat.stat-mech↗

arXiv2025

Nonequilibrium Work Fluctuations in Force-induced Melting of a Short B-DNA

A system of a solvated canonical B-DNA of 12 base pairs with the specified sequence is initially equilibrated in a state of zero external force $f$ acting on it. After equilibration, a switching experiment is performed over the system by pulling one end of the DNA while restraining its other end. The finite time pulling process is performed at a constant rate of the applied force until a maximum value of 400 pN. The associated nonequilibrium work done $(W)$ during this process is determined by numerically integrating the force-extension curve as a function of the applied force. An ensemble of the work values, $P(W)$, is obtained by repeating the pulling experiment a large number of times. We determine the free energy difference $(ΔF)$ between the equilibrium and force-induced melted states of the DNA by employing the Jarzynski equality. The value of $ΔF$ is found to be in close agreement with the conventional equilibrium methods.

cond-mat.soft↗

arXiv2025

Growth Laws and Universality in 2-TIPS: Microscopic and Coarse grained approach

Two temperature induced phase separation(2-TIPS) is a phenomenon observed in mixtures of active and passive particles modeled by scalar activity where the temperature of the particle is proportional to its activity. The binary mixture of 'hot' and 'cold' particles phase separate when the relative temperature difference between hot and cold particles defined as activity $χ$ exceeds a density dependent critical value. The study of kinetics in 2-TIPS, a non-equilibrium phase separation, is of fundamental importance in statistical physics. In this paper, we investigate 2-TIPS kinetics using molecular dynamics (MD) and coarse-grained (CG) modeling in 3D and 2D. The coarse-grained model couples two passive Model B equations for hot and cold particles, with coupling terms emulating the energy transfer between them by raising the temperature of cold particles and lowering that of hot particles, a key observation from the MD simulations. MD simulations reveal that at high densities, phase separation begins immediately after the quench, forming bi-continuous domains rich in hot or cold particles, similar to spinodal decomposition in passive systems. These interconnected domains are also observed in the coarse-grained model for the mixture's critical composition. Both MD and CG models show dynamic scaling of the correlation function, indicating self-similar domain growth. Regardless of dimensionality, both methods report algebraic growth in domain length with a growth exponent of $1/3$, known as the Lifshitz-Slyozov exponent, widely observed in passive systems. Our results demonstrate that the universality of phase separation kinetics observed in passive systems also extends to the non-equilibrium binary mixture undergoing 2-TIPS.

cond-mat.soft↗

arXiv2025

Melting of rods on a sphere via an intermediate hexatic phase

We have studied, using molecular dynamics simulations, the pressure-induced melting in a monolayer of soft repulsive spherocylinders whose centers of mass are constrained to move on the surface of a sphere. We show that the orientational degrees of freedom of the spherocylinders exhibit nematic order, whereas the positions of their centers of mass exhibit melting transitions that depend on the radius of the confining spherical surface. Our system presents a unique scenario where the decoupling of the orientational degrees of freedom from the positional degrees of freedom leads to an effectively two-dimensional (2D) crystal-to-liquid transition on a spherical surface. Further study of the nature of this 2D melting on a sphere shows that the transition is a two-step process, and there exists a very small window of an intermediate hexatic phase between crystal and liquid phases. Similar results are found for flat monolayers (with the radius of the sphere $ R \rightarrow \infty $). We show that, interestingly, the structure of the defects, originating from the curvature of the substrate, also changes during melting.

cond-mat.soft↗

arXiv2025

Freezing in flat monolayers of soft spherocylinders

Lamellar or smectic phases often have an intricate intralamellar structure that remains scarcely understood from a microscopic viewpoint. In this work, we use molecular dynamics simulations to study the effect of volume exclusion and electrostatic repulsion on the phase transitions of a flat membrane of soft spherocylinders. With increasing rod packing, we identify nematic and solid phases and find that the nematic-crystal phase transition happens at a uniform packing fraction ($η_c \approx 0.82$), independent of the spherocylinder aspect ratio. This value is considerably higher than the well-known critical freezing transition of a hard disk fluid ($η_c \approx 0.7$) to which one could naively map a system of near-parallel rods with co-planar mass centers. We attribute this difference to a non-vanishing residual orientational entropy per rod. Our findings are corroborated by a simple theory based on a simple microscopic density functional theory of freezing of a two-dimensional rod fluid. Introduction of electrostatic interactions between the rods reduces the lateral compressibility of the monolayer fluid but keeps the positional order unhindered, which in turn maintains the packing fraction at the nematic-crystal transition. The strength of the orientational fluctuations of the individual rods in our membranes exhibits a density scaling that differs from 3D bulk smectics. Our findings contribute to a qualitative understanding of liquid crystal phase stability in strong planar confinement and engage with recent experimental explorations involving nanorods on 2D substrates.

cond-mat.soft↗

arXiv2024

Deciphering Interstellar Ice Morphology: Atomistic Simulations Reveal the Complex Behavior of Ethanethiol

Ethanethiol (C$_2$H$_5$SH), a molecule detected in the interstellar medium (ISM), indicates the rich chemistry involving sulfur atoms. However, its behavior at low temperatures remains elusive, particularly the reported transition from an amorphous phase to a crystal. This study employs classical molecular dynamics (MD) simulations to reproduce the liquid-state properties of ethanethiol and to simulate the initial amorphous state of ethanethiol films deposited on a KBr substrate. The amorphous ethanethiol did not show spontaneous crystallization upon increasing temperature. Also, ethanethiol ice crystals exhibit melting behavior on KBr substrate at elevated temperatures. Our MD simulations of thin ice samples do not show any signature reversible phase change. It will be interesting to continue this study with a thicker sample, which is beyond our current computational means. These findings underscore the complexity of icy mantle morphology on cold ISM dust grains.

astro-ph.GA↗

arXiv2024

Unifying Mixed Gas Adsorption in Molecular Sieve Membranes and MOFs using Machine Learning

Recent machine learning models to accurately obtain gas adsorption isotherms focus on polymers or metal-organic frameworks (MOFs) separately. The difficulty in creating a unified model that can predict the adsorption trends in both types of adsorbents is challenging, owing to the diversity in their chemical structures. Moreover, models trained only on single gas adsorption data are incapable of predicting adsorption isotherms for binary gas mixtures. In this work, we address these problems using feature vectors comprising only the physical properties of the gas mixtures and adsorbents. Our model is trained on adsorption isotherms of both single and binary mixed gases inside carbon molecular sieving membrane (CMSM), together with data available from CoRE MOF database. The trained models are capable of accurately predicting the adsorption trends in both classes of materials, for both pure and binary components. ML architecture designed for one class of material, is not suitable for predicting the other class, even after proper training, signifying that the model must be trained jointly for proper predictions and transferability. The model is used to predict with good accuracy the CO2 uptake inside CALF-20 framework. This work opens up a new avenue for predicting complex adsorption processes for gas mixtures in a wide range of materials.

cond-mat.soft↗

arXiv2024

Ab initio Investigation of Thermal Transport in Insulators: Unveiling the Roles of Phonon Renormalization and Higher-Order Anharmonicity

The occurrence of thermal transport phenomena is widespread, exerting a pivotal influence on the functionality of diverse electronic and thermo-electric energy-conversion devices. The traditional first-principles theory governing the thermal and thermodynamic characteristics of insulators relies on the perturbative treatment of interatomic potential and ad-hoc displacement of atoms within supercells. However, the limitations of these approaches for highly anharmonic and weakly bonded materials, along with discrepancies arising from not considering explicit finite temperature effects, highlight the necessity for a well-defined quasiparticle approach to the lattice vibrations. To address these limitations, we present a comprehensive numerical framework in this study, designed to compute the thermal and thermodynamic characteristics of crystalline semiconductors and insulators. The self-consistent phonon renormalization method we have devised reveals phonons as quasiparticles, diverging from their conventional characterization as bare normal modes of lattice vibration. The extension of the renormalization impact to interatomic force constants (IFCs) of third and fourth orders is also integrated and demonstrated. For the comprehensive physical insights, we employed an iterative solution of the Peierls-Boltzmann transport equation (PBTE) to determine thermal conductivity and carry out Helmholtz free energy calculations, encompassing anharmonicity effects up to the fourth order. In this study, we utilize our numerical framework to showcase its applicability through an examination of phonon dispersion, phonon linewidth, anharmonic phonon scattering, and temperature-dependent lattice thermal conductivity in both highly anharmonic materials (NaCl and AgI) and weakly anharmonic materials (cBN and 3C-SiC).

cond-mat.mtrl-sci↗

arXiv2023

Stability of chiral crystal phase and breakdown of cholesteric phase in mixtures of active-passive chiral rods

In this study, we aim to explore the effect of chirality on the phase behavior of active helical particles driven by two-temperature scalar activity. We first calculate the equation of state of soft helical particles of various intrinsic chiralities using molecular dynamics (MD) simulation. In equilibrium, the emergence of various liquid crystal (LC) phases such as nematic (N), cholesteric ($N_{c}^{*}$), smectic (Sm), as well as crystal (K), crucially depends on the presence of the walls, which induce homeotropic alignment. Next, we introduce activity through the two-temperature model: keep increasing the temperature of half of the helical particles (labeled as 'hot' particles) while maintaining the temperature of the other half at a lower value (labeled as 'cold' particles). Starting from a homogeneous isotropic (I) phase, we find the emergence of 2-TIPS: two temperature-induced phase separations between the hot and cold particles. We also observe the cold particles undergo an ordering transition to various LC phases even in the absence of a wall. This observation reveals that the hot-cold interface in the active system plays the role of a wall in the equilibrium system by inducing an alignment direction for the cold particles. However, in the case of a cholesteric phase, we observe activity destabilizes the $N_{c}^{*}$ phase by inducing smectic ordering in the cold zone while isotropic structure in the hot zone. The smectic ordering in the cold zone eventually transforms to a chiral crystal phase at high enough activity.

cond-mat.soft↗

arXiv2023

Trajectory Extending Kinetic Monte Carlo Simulations to Evaluate Pure and Gas Mixture Diffusivities through a Dense Polymeric Membrane

With renewed interest in CO2 separations, carbon molecular sieving (CMS) membrane performance evaluation requires diffusion coefficients as inputs to have reliable estimate of the permeability. An optimal material is desired to have both high selectivity and permeability. Gases diffusing through dense, CMS and polymeric membranes experience extended sub-diffusive regimes which hinders reliable extraction of diffusion coefficients from mean squared displacement data. We improve the sampling of the diffusive landscape by implementing the trajectory extending kinetic Monte Carlo (TEKMC) technique to efficiently extend MD trajectories from ns to μs timescales. The obtained self-diffusion coefficient of pure CO2 in CMS membranes derived from 6FDA/BPDA-DAM precursor polymer melt is found in agreement with previous experimental findings. We also extend the TEKMC algorithm to evaluate the mixture diffusivities in binary mixtures to determine the permselectivity of CO2 in CH4 and N2 mixtures. The mixture diffusion coefficient of CO2 ranges from 1.3-7 x 10^{-6} cm6{2}s^{-1} in binary mixture CO2:CH4 which is significantly higher than the pure gas diffusion coefficient. Robeson plot comparisons show that the permselectivity obtained from pure gas diffusion data are significantly lower than that predicted using mixture diffusivity data. Specifically in the case of the CO2:N2 mixture we find that using mixture diffusivities led to permeslectivites lying above the Robeson limit highlighting the importance of using mixture diffusivity data for an accurate evaluation of the membrane performance. Combined with gas solubilities obtained from grand-canonical Monte Carlo simulations, our work shows that simulations with the TEKMC method can be used to reliably evaluate the performance of materials for gas separations.

cond-mat.soft↗