arXiv subjects

David T. Limmer

Publications and source records attributed to David T. Limmer.

At least 19 recordsLinked to original sources

arXiv2026

Size-Dependent Growth Rates Amplify Infinitesimal Asymmetry in Nanocrystals

The kinetic Wulff construction predicts symmetric nonequilibrium shapes when crystallographically equivalent facets share a fixed growth rate. However, nanocrystals grow through finite facets whose nucleation barriers and ligand coverages depend on facet size. Here we develop a size-dependent kinetic construction and show that as a consequence infinitesimal seed asymmetries can be amplified into strongly asymmetric nanocrystal morphologies even when all symmetry-related facets obey the same microscopic growth law. Spatially heterogeneous nucleation rates and boundary limited growth generate facet growth velocities that depend on size, and deterministic shape evolution translates these local rates into global shape symmetry breaking. We illustrate the mechanism of persistent anisotropic growth on square and triangular lattices in two dimensions and on FCC seeds in three dimensions, where cuboctahedra can evolve toward rods or tetrahedra depending on which facet-area perturbations are amplified.

cond-mat.mtrl-sci↗

arXiv2026

Entropy Production Bounds the Accuracy of Computation in Markov Networks

Biological and artificial networks compute by transforming time-dependent inputs into functional outputs. Because the internal state of a stochastic network relaxes on finite timescales, its output generally lags behind a changing environment, producing computational errors. We show that for reversible continuous-time Markov networks the error admits a universal thermodynamic bound. Decomposing the total error into representation and lag contributions, we derive an inequality relating the lag error to the entropy production rate and a memory time equal to the integrated equilibrium autocorrelation of the output observable. The bound implies that accurate dynamical computation requires either substantial dissipation or long-lived memory encoded in slowly relaxing modes. We demonstrate these principles in artificial Markov networks and in models of biochemical information processing. Our results establish a thermodynamic limit on information processing in stochastic networks and provide a quantitative framework for understanding the energetic costs of biological computation.

cond-mat.stat-mech↗

arXiv2026

Odd Diffusion in Three-Dimensional Isotropic Media

Odd diffusion is a hallmark of chiral active matter, generating currents transverse to density gradients. Existing theories rely on a linear antisymmetric transport coefficient that exists only in two dimensions, raising the question of whether odd diffusion can occur in isotropic three-dimensional systems. Here we show that such transport is possible through a nonlinear constitutive law. Symmetry considerations reveal that the three-dimensional Levi-Civita tensor permits a leading order isotropic odd current at second order in the density gradient expansion and only in multicomponent systems. The resulting transport generates boundary-driven rotational currents, finite vorticity, and enstrophy despite the absence of external torques or preferred directions. We show how such a constitutive law derives from a microscopic model of particles interacting through nonreciprocal three-body forces using the Dean--Kawasaki coarse-graining procedure. These results establish a minimal framework for odd transport in isotropic three dimensions.

cond-mat.soft↗

arXiv2026

Origins of suppressed self-diffusion of nanoscale constituents of a complex liquid

Understanding and ultimately controlling the transformations and properties of nanoscale systems, from proteins to synthetic nanomaterial assemblies, is limited by the inability to uncover their dynamics on their characteristic length and time scales. Here, we nevertheless demonstrate this ability using MHz X-ray photon correlation spectroscopy (XPCS) -- directly elucidating the characteristic microsecond-dynamics of density fluctuations of semiconductor nanocrystals (NCs), not only in a colloidal dispersion but also in a liquid phase consisting of densely packed, yet mobile, NCs with no long-range order. We find the wavevector-dependent fluctuation rates in the liquid phase are suppressed relative to those in the colloidal phase and relative to observations of densely packed repulsive particles. We show that the suppressed rates are due to a substantial decrease in the self-diffusion of NCs, which we attribute to explicit attractive interactions. Using coarse-grained simulations, we find that the extracted shape and strength of the interparticle potential explains the stability of the liquid phase, in contrast to the gelation observed via XPCS in many other charged colloidal systems. This work opens the door to elucidating fast, condensed phase dynamics in complex fluids and other nanoscale soft matter, such as densely packed proteins and non-equilibrium self-assembly processes, in addition to designing microscopic strategies to avert gelation.

cond-mat.soft↗

arXiv2026

Solvent Effects on Triplet Yields in BODIPY-Based Photosensitizers

We employ molecular dynamics simulations and quantum rate theories to elucidate the complex condensed-phase dynamics underpinning triplet-state formation in organic photosensitizers. Using models informed by first-principles calculations complete with a molecular representation of solvents of different polarities, we elucidate the interplay of the internal and environmental interactions underlying triplet yield. We find that triplet yields depend sensitively on the dielectric stabilization of the charge transfer intermediate that facilitates a transition into the triplet manifold. Our results illustrate the importance of molecularly detailed models in understanding the excited-state internal charge-transfer dynamics of photochemically-relevant organic molecules.

physics.chem-ph↗

arXiv2026

Visualizing Millisecond Atomic Dynamics of Nanocrystals in Liquid

Atomic structures of nanomaterials are inherently dynamic, continuously reshaped through interactions with chemical species and external stimuli. Such dynamics are further amplified as the size and dimensionality of nanomaterials are reduced. Despite advances in analytical methods, it remains challenging to capture structural dynamics of nanomaterials in reactive environments with both atomic spatial resolution and commensurate temporal resolution. Here, we directly visualize atomic-scale dynamics of gold (Au) nanocrystals in reactive liquid environments with millisecond-speed liquid cell electron microscopy (EM) and deep-learning denoising. We uncover reversible fluctuations in local crystallinity of Au nanocrystals dependent on the surrounding chemical environment. These transient fluctuations, driven by interactions at nanocrystal-liquid interfaces, critically influence dissolution kinetics and grain boundary relaxation. By overcoming the spatiotemporal limitations in conventional liquid cell EM, our findings provide insights into how transient nanoscale structures dictate the stability and reactivity of nanomaterials.

cond-mat.mtrl-sci↗

arXiv2026

Influence Functional Approach to Non-Perturbative Exciton Binding Renormalization from Phonons

We construct a many-body model Hamiltonian to capture how phonons renormalize exciton binding as a function of temperature. By using the GW approximation and density functional perturbation theory, we are able to parameterize this Hamiltonian completely from first principles. To capture static quasiparticle properties non-perturbatively, we evolve this Hamiltonian in imaginary time with path integral Monte Carlo using an influence functional based approach. For a class of Wannier-Mott type excitons, our binding energies are in quantitative agreement with experiment. We find that in addition to long-range dipolar interactions from longitudinal optical modes, short-ranged deformation potentials from acoustic modes and transverse optical modes can significantly renormalize electron and hole polaron binding energies at elevated temperature. However, exciton binding energies are only appreciably renormalized by coupling to optical phonons.

cond-mat.mtrl-sci↗

arXiv2026

Origin of Edge Currents in Chiral Active Liquids

Chiral active liquids generically exhibit unidirectional edge currents in confinement. While this phenomenon has been attributed to model-specific mechanisms and interpreted through phenomenological equations, a universal understanding of it, and its connection to microscopic dynamics remain absent. Starting from the microscopic equations of motion of a simple interacting two-dimensional model, we find that localized edge currents emerge as a consequence of global angular momentum balance. From these underlying equations, we derive an Ohmic-like conductance law for the mean edge current in the dense phase, and we find it to be intensive, depending only on the density, active torque and substrate drag. For simple geometries, we find the distribution of the edge currents has a closed Gaussian form, with a variance that is intensive, depending only on temperature, density and the aspect ratio of the system. These results are validated numerically using extensive molecular dynamics simulations. This origin of the edge current is shown to extend to other models of chiral systems where angular momentum is injected in distinct ways.

cond-mat.soft↗

arXiv2026

Pattern stability in reaction-diffusion systems depends on path entropy

Reaction-diffusion systems driven far from thermodynamic equilibrium through the injection of energy can support multiple distinct spatial patterns that persist as long-lived dynamical phases. The stability of these metastable phases is not determined by thermodynamics, but by the transition paths connecting them. At finite particle numbers, intrinsic stochasticity induces rare transitions between competing patterns, rendering continuum mean-field descriptions insufficient, while exact stochastic simulations become computationally prohibitive in spatially extended systems. Here, we develop a nonequilibrium instanton framework that enables efficient computation of transition rates between metastable patterns from a single optimal transition path and its fluctuations. Using this theoretical framework, we show that an effective entropy in path space can qualitatively alter stability at finite particle numbers by increasing the exit rates of metastable patterns. By studying models of varying complexity, this work establishes path entropy as a key organizing principle for nonequilibrium pattern formation.

cond-mat.stat-mech↗

arXiv2026

Spin Polarization from Circularly Polarized Light Induced Charge Transfer

We show how a spin polarization can be generated through the photo-induced electron transfer of an achiral donor-acceptor complex following chiral light excitation. In particular, we illustrate the basic energetic and symmetry requirements for chirality induced spin selectivity where the chirality emerges from the electronic degrees of freedom following excitation with circularly polarized light. We study this effect in a simple model of a metalloporphyrin complex with an axial acceptor ligand using quantum mechanical rate theories and numerical simulations. We find that the spin polarization emerges due to the selective excitation of a ring current within the porphryin, breaking the degeneracy of the two degenerate spin states. The resultant spin polarization increases with the spin orbit coupling between the metal in the porphyrin and the axial ligand, and is transient, with a lifetime dependent on the rate of dephasing from the Jahn-Teller distortion mode. This proposed effect should be observable in spin-resolved photoemission spectroscopy.

physics.chem-ph↗

arXiv2026

Field-driven Ion Pairing Dynamics in Concentrated Electrolytes

We investigate ion pairing dynamics in electrolytes driven far from equilibrium using molecular simulations and nonequilibrium rate theory. Focusing on 0.5 M $\mathrm{LiPF_6}$ in water and acetonitrile under uniform electric fields, we compute transition path theory observables including reactive fluxes and mean first-passage times of ion pairing. Moreover, we introduce a dynamical proxy of free-ion population, where its field-induced change is strongly correlated with the nonlinear enhancement of conductivity, yielding an increase of $40 \ \%$ at 50 mV/Å in acetonitrile, compared to less than $10 \ \%$ in aqueous electrolytes. Further kinetic analysis elucidates that Onsager's classical theory substantially overestimates field-induced enhancement of ion pair dissociation in molecular electrolytes. This discrepancy arises from solvent-mediated dynamical pathways and field-induced dielectric decrement that suppress ion pair dissociation within explicit solvents, highlighting that a faithful description of molecular details is essential. Our results provide a molecular interpretation of nonlinear electrolyte transport beyond continuum theories and establish a general framework for quantifying nonequilibrium reaction kinetics in condensed phase systems.

physics.chem-ph↗

arXiv2026

Optimal control of bit erasure in stochastic random access memory

Energy costs of information processing are growing exponentially. Bit erasure is a key problem in this energy-information nexus, and a number of seminal relationships have been deduced regarding the relationship between thermodynamic costs and memory storage. To continue making progress in the modern era, however, requires confronting thermodynamic costs in realistic physical systems which operate away from equilibrium. Here, we explore the thermodynamic costs of bit erasure in a complementary metal oxide semiconductor model of two types of random access memory. We find dynamic random access memory dissipates the least amount of energy when operated in the quasistatic limit, where errors are also minimized. By contrast, static random access memory is most efficiently operated in finite time due to the energy required to maintain the state of the bit. We demonstrate a numerically robust optimization scheme using mean field theory and automatic differentiation, finding optimal protocols compatible with electrical engineering insights. These results provide a framework for operating realistic circuits in thermodynamically advantageous ways.

cond-mat.stat-mech↗

arXiv2026

Atomic Alignment in PbS Nanocrystal Superlattices with Compact Inorganic Ligands via Reversible Oriented Attachment of Nanocrystals

Nanocrystals (NCs) serve as versatile building blocks for the creation of functional materials, with NC self-assembly offering opportunities to enable novel material properties. Here, we demonstrate that PbS NCs functionalized with strongly negatively charged metal chalcogenide complex (MCC) ligands, such as $Sn_2S_6^{4-}$ and $AsS_4^{3-}$, can self-assemble into all-inorganic superlattices with both long-range superlattice translational and atomic-lattice orientational order. Structural characterizations reveal that the NCs adopt unexpected edge-to-edge alignment, and numerical simulation clarifies that orientational order is thermodynamically stabilized by many-body ion correlations originating from the dense electrolyte. Furthermore, we show that the superlattices of $Sn_2S_6^{4-}$-functionalized PbS NCs can be fully disassembled back into the colloidal state, which is highly unusual for orientationally attached superlattices with atomic-lattice alignment. The reversible oriented attachment of NCs, enabling their dynamic assembly and disassembly into effectively single-crystalline superstructures, offers a pathway toward designing reconfigurable materials with adaptive and controllable electronic and optoelectronic properties.

cond-mat.mtrl-sci↗

arXiv2026

Nanocrystal Geometry Governs Phase Transformation Pathways in Palladium Hydride

Pathways and structural dynamics of phase transformations impact performance of materials in energy and information storage technologies. Palladium hydride ($\mathrm{PdH}_x$) nanocrystals are an ideal model system for studying solute-induced phase transformations, where elastic energy from lattice mismatch between $α$-$\mathrm{PdH}_x$ and $β$-$\mathrm{PdH}_x$ phases is often considered a key to determining the transformation pathways. $α/β$-$\mathrm{PdH}_x$ interfacial elastic energy is affected by the confined geometry of a nanocrystal. However, how nanocrystal geometry influences phase transformation pathways is largely unknown. Using in situ liquid phase transmission electron microscopy, we directly visualize hydrogenation in Pd nanocrystals with two geometries -- a nanocube and a hexagonal nanoplate. Both follow similar sequences of an initially curved nucleus, interface flattening, and reverse-stage nucleation; however, their evolving $α/β$-$\mathrm{PdH}_x$ interfaces exhibit geometry-dependent crystallographic alignments. In nanocubes, $\{100\}$-aligned configurations conform to static elastic energy ordering, representing a pathway that maintains a local mechanical equilibrium, whereas nanoplates display both $\{110\}$- and $\{211\}$-aligned interfaces. Theoretical simulations show that geometry determines the accessibility of alternative phase transformation pathways as the system is driven far from equilibrium during hydrogenation. These findings identify geometry as a fundamental parameter for directing phase transformation pathways, offering design principles for accessing atypical configurations and improving properties of intercalation-based devices.

cond-mat.mes-hall↗

arXiv2025

Nonadiabatic force matching for alchemical free-energy estimation

We propose a method to compute free-energy differences from nonadiabatic alchemical transformations using flow-based generative models. The method, nonadiabatic force matching, hinges on estimating the dissipation along an alchemical switching process in terms of a nonadiabatic force field that can be learned through stochastic flow matching. The learned field can be used in conjunction with short-time trajectory data to evaluate upper and lower bounds on the alchemical free energy that variationally converge to the exact value if the field is optimal. Applying the method to evaluate the alchemical free energy of atomistic models shows that it can substantially reduce the simulation cost of a free-energy estimate at negligible loss of accuracy when compared with thermodynamic integration.

physics.chem-ph↗

arXiv2025

Electronic origin of reorganization energy in interfacial electron transfer

Electron transfer (ET) reactions underpin energy conversion and chemical transformations in both biological and abiological systems. The efficiency of any ET process relies on achieving a desired ET rate within an optimal driving force range. Marcus theory provides a microscopic framework for understanding the activation free energy, and thus the rate, of ET in terms of a key parameter: the reorganization energy. For electrified solid-liquid interfaces, it has long been conventionally understood that only factors in the electrolyte phase are responsible for determining the reorganization energy and the electronic density of states (DOS) of the electrode serves only to dictate the number of thermally accessible channels for ET. Here we show instead that the electrode DOS plays a central role in governing the reorganization energy, far outweighing its conventionally assumed role. Using atomically layered heterostructures, we tune the DOS of graphene and measure outer-sphere ET kinetics. We find the ensuing variation in ET rate arises from strong modulation in a reorganization energy associated with image potential localization in the electrode. This work redefines the traditional paradigm of heterogeneous ET kinetics, revealing a deeper role of the electrode electronic structure in interfacial reactivity.

cond-mat.mtrl-sci↗

arXiv2025

Large deviations of ionic currents in dilute electrolytes

We evaluate the exponentially rare fluctuations of the ionic current for a dilute electrolyte by means of macroscopic fluctuation theory. We consider the fluctuating hydrodynamics of a fluid electrolyte described by a stochastic Poisson-Nernst-Planck equation. We derive the Euler-Lagrange equations that dictate the optimal concentration profiles of ions conditioned on exhibiting a given current, whose form determines the likelihood of that current in the long-time limit. For a symmetric electrolyte under small applied voltages, number density fluctuations are small, and ionic current fluctuations are Gaussian with a variance determined by the Nernst-Einstein conductivity. Under large applied potentials, where number densities vary, the ionic current distribution is generically non-Gaussian. Its structure is constrained thermodynamically by Gallavotti-Cohen symmetry and the thermodynamic uncertainty principle.

cond-mat.stat-mech↗

arXiv2025

Theoretical insights into the role of lattice fluctuations on the excited behavior of lead halide perovskites

Lead halide perovskites have been extensively studied as a class of materials with unique optoelectronic properties. A fundamental aspect that governs optical and electronic behaviors within these materials is the intricate coupling between charges and their surrounding lattice. Unravelling the role of charge-lattice interactions on the optoelectronic properties in lead halide perovskites is necessary to understand their photophysics. Unlike traditional semiconductors where a harmonic approximation often suffices to capture lattice fluctuations, lead halide perovskites have a significant anharmonicity attributed from the rocking and tilting motions of inorganic framework. Thus, while there is broad consensus on the importance of the structural deformations and polar fluctuations on the behavior of charge carriers and quasiparticles, the strongly anharmonic nature of these fluctuations and their strong interactions render theoretical descriptions of lead halides perovskites challenging. In this Account, we review our recent efforts to understand how the soft, polar lattice of this class of materials alter their quasiparticle binding energies and fine structure, charge mobilities, and lifetimes of phonons and excess charges. Throughout, these are aimed at characterizing the interplay between lattice fluctuations and optoelectronic properties of lead halide perovskites and are reviewed in the context of the effective models we have built, and the novel theoretical methods we have developed to understand bulk crystalline materials, as well as nanostructures, and lower dimensionality lattices. By integrating theoretical advances with experimental observations, the perspective we detail in this account provides a comprehensive picture that serves as both design principles for optoelectronic materials and a set of theoretical tools to study them when charge-lattice interactions are important.

cond-mat.mtrl-sci↗