Browse Articles

Dollar Dominance and the Transmission of Monetary Policy

Abstract Has the dominance of the dollar in global trade rendered monetary policy ineffective? An emerging view contends that if a country invoices its exports in dollars, exchange rates cannot stabilize economic activity, as the classical expenditure-switching channel is muted. This view rests on the premise that export prices are sticky in dollars, breaking the link between export demand and depreciations. But this assumption is not borne out by the data: goods priced in dollars tend to have more flexible prices, along with higher elasticities of substitution. We propose a model with more realistic assumptions and show that even with dollar pricing, depreciating the currency by loosening monetary policy can still boost exports and activity materially. The limit to any expansion is not demand, but supply capacity. We also show that low exchange rate pass-through to dollar prices is not informative about price stickiness. The price response to exchange rates is small when demand elasticities are high, even with flexible prices: low pass-through is an equilibrium result, not evidence of a nominal friction.

Polymorph selection in charged colloids in the second nucleation step

We study polymorph selection in a model of charged colloids, with a focus on the higher-order structure prior to and during nucleation. Specifically, we carry out molecular dynamics simulations of a repulsive Yukawa system with a slightly softened (Weeks–Chandler–Andersen) core. We consider the case where the interaction is long-ranged and the BCC crystal is stable, and also intermediate- and short-ranged cases where the FCC crystal is stable. We use two methods for structure identification, the topological cluster classification (TCC) [A. Malins et al., J. Chem. Phys. 139, 234506 (2013)] and the bond orientational order parameter analysis of Lechner and Dellago [J. Chem. Phys. 129, 114707 (2008)]. Under conditions of high supersaturation appropriate to experiments with colloids, we find that the system forms a precursor state in which the particles are hexagonally ordered. That is to say, the precursors are indistinguishable from an HCP crystal using the bond orientational order parameters. This ordering occurs at state points when the body-centered cubic crystal is the stable phase and also when the face-centered cubic crystal is stable. In all cases, the stable polymorph forms from the precursor phase in a second stage. Although at freezing the fluid is much more ordered when the interactions are short-ranged (when FCC is stable), at the supersaturations where nucleation occurs in our simulations, the higher-order structure of the metastable fluids is almost identical for the long-, short-, and intermediate-ranged systems when measured with the TCC.

Failing Banks

Abstract Why do banks fail? We create a panel covering most commercial banks from 1863 through 2024 to study the history of failing banks in the United States. Failing banks are characterized by rising asset losses, deteriorating solvency, and an increasing reliance on expensive noncore funding. These commonalities imply that bank failures are highly predictable using simple accounting metrics from publicly available financial statements. Failures with runs were common before deposit insurance, but these failures are strongly related to weak fundamentals, casting doubt on the importance of non-fundamental runs. Furthermore, low recovery rates on failed banks’ assets suggest that most failed banks subject to runs were fundamentally insolvent, barring large value destruction of receiverships. Altogether, our evidence suggests that the primary cause of bank failures and banking crises is almost always and everywhere a deterioration of bank fundamentals.

Path-integral calculation of the second and third density virial coefficients of 4He

We present a comprehensive study of the second and third density virial coefficients, B(T) and C(T), of 4He across an extended temperature range from 1 K to 10 000 K, utilizing the path-integral Monte Carlo (PIMC) method and the most accurate interaction potentials. This work reports the first complete determination of B(T) within the PIMC framework, demonstrating excellent agreement and comparable uncertainties with results from the established phase-shift method, thus providing crucial cross-method validation. We generate a significantly extended and high-accuracy dataset for C(T), complementing existing literature values. A comprehensive uncertainty analysis quantifies contributions from both two-body and three-body potentials. The results reveal subtle differences from previous work for C(T) below 5 K, while reducing the uncertainty by approximately a factor of two in this low-temperature regime. This study provides crucial reference data to enhance the accuracy of primary standards for both temperature and pressure based on 4He.

Political Foundations of Racial Violence in the Post-Reconstruction South

Abstract Election results act as powerful signals, shaping social behavior in ways that can be dramatic and even violent. This article shows how racial violence in the post-Reconstruction U.S. South was tied to the local performance of the anti-Black Democratic Party in presidential elections. Using a regression discontinuity design based on close presidential vote shares, we find that Southern counties where Democrats lost the popular vote between 1880 and 1900 were nearly twice as likely to experience Black lynchings in the following four years. Despite no corresponding changes in local office holding, these defeats were salient among local elites. We show that Southern newspapers, closely aligned with the Democratic Party, amplified narratives of Black criminality in the aftermath of Democratic losses. Such accusations were, in turn, frequently invoked by lynch mobs. These findings point to the strategic use of racial violence by Democratic elites, foreshadowing the institutionalized vote suppression of Jim Crow.

Electron transfer in confined electromagnetic fields: A unified Fermi’s golden rule rate theory and extension to lossy cavities

With the rapid development of nanophotonics and cavity quantum electrodynamics, there has been growing interest in how confined electromagnetic fields modify fundamental molecular processes such as electron transfer. In this paper, we revisit the problem of nonadiabatic electron transfer (ET) in confined electromagnetic fields studied in Semenov and Nitzan [J. Chem. Phys. 150, 174122 (2019)] and present a unified rate theory based on Fermi’s golden rule. By employing a polaron-transformed Hamiltonian, we derive analytic expressions for the ET rate correlation functions that are valid across all temperature regimes and all cavity mode time scales. In the high-temperature limit, our formalism recovers the Marcus and Marcus–Jortner results, while in the low-temperature limit, it reveals the emergence of the energy gap law. We further extend the theory to include cavity loss by using an effective Brownian oscillator spectral density, which enables closed-form expressions for the ET rate in lossy cavities. As applications, we demonstrate two key cavity-induced phenomena: (i) resonance effects, where the ET rate is strongly enhanced with certain cavity mode frequencies, and (ii) electron-transfer-induced photon emission, arising from the population of cavity photon Fock states during the ET process. These results establish a general framework for understanding how confined electromagnetic fields reshape charge transfer dynamics and suggest novel opportunities for controlling and probing ET reactions in nanophotonic environments.

Ideas Have Consequences: The Impact of Law and Economics on American Justice

Abstract This article empirically studies the effects of the early law and economics movement on the U.S. judiciary. We focus on the Manne Economics Institute for Federal Judges, an intensive economics course that trained almost half of federal judges between 1976 and 1999. Using the universe of published opinions in U.S. Circuit Courts and 1 million District Court criminal sentencing decisions, we estimate the within-judge effect of Manne program attendance. Selection into attendance was limited, as the program was popular among judges of all backgrounds, frequently oversubscribed, and admitted participants on a first-come, first-served basis. We find that after attending economics training, participating judges use more economics language in their opinions, rule against regulatory agencies more often, and impose more severe criminal sentences. We argue that economics, as a rigorous social science, was especially effective in persuading judges.

Effect of polyelectrolyte mixing ratio and hydrophobic interactions on dynamics of (HM-)PDMAEMA/PEO-PMAA complexes

The complexation of oppositely charged polyelectrolytes leads to Polyelectrolyte Complexes (PECs). PECs can exist in many different states, depending on the architecture of the polymers and the environmental parameters of the solution. Using double hydrophilic block copolymers (DHBCs), PECs can be stabilized as dispersed aggregates in solutions. Specifically, the polymers involved in this investigation are a DHBC composed of a poly(ethylene glycol) block and a poly(methacrylic acid) block (PEO-PMAA) used as the polyanion and poly(2-(dimethylamino)ethyl methacrylate), with and without hydrophobic dodecyl substitutions, used as the polycation. In this paper, we discuss the behavior of the nanoscale dynamics with respect to their mixing ratio. We also test the impact of hydrophobic modifications on the dynamics of the aggregates. By neutron spin echo spectroscopy and neutron backscattering spectroscopy, we observed the role of electrostatic interaction as a friction induced on the polymers, where complexation leads to slower diffusion and the hydrophobic moieties affect the rigidity of the polymers.

Traditional Institutions in Modern Times: Dowries as Pensions When Sons Migrate

Abstract This paper uses newly collected data on the allocation of dowry to examine its role in resolving intergenerational frictions around migration in India. Migration disrupts traditional elderly support structures, in which sons live near their parents and care for them in old age. We develop a model in which dowry can promote migration by allowing sons to make upfront transfers to their parents and ease constraints on income sharing. To test this hypothesis, we collect two new data sets that measure the distribution of dowry between family members. We document for the first time that net transfers of dowry to a man’s parents are common but far from universal. Consistent with using dowry for income sharing, such transfers occur more often when sons migrate, especially when they work in higher-earning occupations. In nationally representative data, migration rates are higher in areas with stronger historical dowry traditions. Finally, exploiting a large-scale highway construction program, we show that men from areas with stronger historical dowry traditions migrate more when migration costs fall. Our findings provide some clues as to why dowry persists despite its well-documented adverse consequences.

Definitions of atoms in molecules with the modified Dirac equations

In this work, we present calculations of the basins and electronic population at the relativistic level, with expressions derived from a total Lagrangian density associated with the modified Dirac Hamiltonian [Zapata-Escobar and Maldonado, J. Chem. Phys. 163, 024310 (2025)]. Calculations were carried out using a local implementation for the numerical construction of the basins and the corresponding integrations of the electronic population. The basins’ evaluation and electronic population calculations were obtained on both relativistic and nonrelativistic expressions, reproducing 99.9% of the total charge in the HX (X = F, Cl, Br, I, At) and SnH4 molecules. We found that the relativistic effects cause a contraction of the electron density around the nuclei of the heavy atoms, while for the hydrogen atom, the electronic population decreases, leading to a decrease in the dipole moment. In addition, we present the continuity equation from the modified Dirac Hamiltonian in order to interpret the scalar field used to obtain the basin with this scheme of calculation. Finally, we propose a new Lagrangian density associated with the Dirac Hamiltonian, from which it is possible to obtain an expression for the zero-flux condition, thereby recovering the nonrelativistic basin expression within the quantum theory of atoms in molecules approach directly from the relativistic formulation without adding a heuristic term.

Open quantum–classical systems: A hybrid MASH master equation

We propose a method that combines the quantum–classical mapping approach to surface hopping with the dissipative quantum dynamics of the Lindblad master equation. Like conventional surface-hopping methods, our approach is based on classical trajectories coupled to the dynamics of a quantum subsystem. However, instead of evolving the subsystem wavefunction according to the time-dependent Schrödinger equation, we use stochastic quantum trajectories derived from secular Redfield theory. This approach enables the simulation of open quantum systems coupled simultaneously to Markovian quantum baths and anharmonic, non-Markovian classical degrees of freedom. Applications to the spin–boson model and to the cavity-enhanced fluorescence of an electronically nonadiabatic molecule show excellent agreement with fully quantum-mechanical benchmarks.

Nonadiabatic H-atom scattering channels on Ge(111) elucidated by the hierarchical equations of motion

Atomic and molecular scattering at semiconductor interfaces plays a central role in surface chemistry and catalysis, yet predictive simulations remain challenging due to strong nonadiabatic effects, causing the breakdown of the Born–Oppenheimer approximation. Here, we present fully quantum simulations of H-atom scattering from the Ge(111)c(2 × 8) rest site using the hierarchical equations of motion (HEOM) with matrix product states. The system is modeled by mapping a density functional theory potential energy surface onto a Newns–Anderson Hamiltonian. Our simulations reproduce the experimentally observed bimodal kinetic energy distributions, capturing both elastic and energy-loss channels. By systematically examining atom–surface coupling, incident energy, and isotope substitution, we identify the strong-coupling regime required to recover the experimental energy-loss profile. This regime suppresses the elastic peak, implying additional site-specific scattering channels in the observed elastic peak. Deuterium substitution further produces a subtle shift in the energy-loss peak, consistent with experiment. These results establish HEOM as a rigorous framework for quantum surface scattering, capable of capturing nonadiabatic dynamics beyond electronic friction and perturbative approaches.

The weakly bound CO molecule adsorbed on the low-index CeO2 surfaces: A case for a CCSD(T) benchmark study using an embedded-cluster model

The binding energy and the vibrational stretching frequency of the probe molecule CO adsorbed on the low-index CeO2 surfaces [(100), (110), and (111)] were benchmarked using the coupled-cluster singles, doubles, perturbative triples [CCSD(T)] method, employing an embedded cluster approach. Using the same methodology as for the top configuration of CO on the (111) surface [J. Vázquez Quesada et al., J. Chem. Phys. 161, 224707 (2024)], the best theoretical estimate for the CO frequency on the CeO2(100) surface (CO bridge configuration) obtained at the CCSD(T)/def2-TZ/QZVPP level of theory and under low-coverage conditions (2193 cm−1) is 17 cm−1 larger than the experimental value (1 ML coverage saturation), which is in agreement with previous estimates for the CO adsorption on the CeO2(111) surface (12 cm−1). For the (110) surface, theoretical and experimental data compare differently. The CCSD(T)/def2-TZ/QZVPP values are −7 cm−1 (top configuration) and −21 cm−1 (tilt-x configuration) lower than the two experimental features measured at 2170 cm−1 (negative feature) and 2160 cm−1 (positive feature). MP2 predictions suggest the existence of a case of multiple-configuration dynamics with various almost isoenergetic configurations in a low-coverage situation. The CO harmonic vibrational frequencies were not semi-empirically scaled but explicitly corrected for anharmonic effects, which amount to 25–26 cm−1 with all tested methods. CO adsorption energies of −0.40 ± 0.07 eV, −0.17 ± 0.07 eV, and −0.20 ± 0.07 eV for the (100), (110) (top), and (110) (tilt-x) adsorption sites, respectively, are obtained at the CCSD(T)/def2-TZ/QZVPP level of theory. These results agree well with those proposed for the (111) surface (−0.22 ± 0.07 eV) [J. Vázquez Quesada et al., J. Chem. Phys. 161, 224707 (2024)] and confirm the physisorption character of the adsorption of CO on the three low-index surfaces of CeO2.

GPU-accelerated continuum dynamics of block copolymer blends and solutions

We present an open-source, graphics processing unit (GPU)-accelerated software implementation of the Uneyama–Doi model (UDM) for studying the collective dynamics of block copolymer blends and solutions. The UDM provides a field-theoretic framework that includes the entropy of mixing, binary interactions between segment species, and molecular connectivity, thereby capturing interfacial properties even in the strong-segregation regime. Our implementation utilizes a semi-implicit time-stepping scheme, incorporates thermal noise, and employs a concentration-conserving regularization algorithm that maintains non-negative concentrations. Spatial derivatives and convolutions are computed via optimized CUDA-based pseudo-spectral methods, enabling simulations of systems spanning tens of polymer end-to-end distances and thousands of molecular relaxation times within hours on a single GPU. We validate the implementation against established results, including the mean-field phase diagram of diblock copolymers, structure factors of disordered systems, and the fluctuation-induced order–disorder transition for symmetric copolymers. Dynamic simulations reproduce experimentally observed amphiphilic morphologies, including micellar lattices, vesicles, and phase-separated structures. The software provides an efficient and versatile tool for investigating equilibrium and nonequilibrium behavior of complex polymer systems.

Thermally Stabilized Hydrogenation Dynamics in Single-Atom Alloys Enables Selective CO ₂ Electroreduction

A Haldane–Anderson Hamiltonian model for hyperthermal hydrogen scattering from a semiconductor surface

Collisions of atoms and molecules with metal surfaces create electronic excitations in the metal, leading to nonadiabatic energy dissipation, inelastic scattering, and sticking. Mixed quantum-classical molecular dynamics simulation methods, such as molecular dynamics with electronic friction, are able to capture nonadiabatic energy loss during dynamics at metal surfaces. Hydrogen atom scattering from semiconductors, on the other hand, exhibits strong adsorbate-surface energy transfer only when the projectile kinetic energy exceeds the bandgap of the substrate. Electronic friction fails to describe this effect. Here, we report a first-principles parameterization of a simple Haldane–Anderson Hamiltonian model of hydrogen atom gas-surface scattering on Ge(111)c(2 × 8), for which hyperthermal scattering experiments have been reported. We subsequently perform independent-electron surface hopping and Ehrenfest dynamics simulations on this model and validate these results through numerically exact quantum-dynamical simulations using the hierarchical equation of motion approach. While mean-field dynamics yield weak nonadiabatic energy loss that is independent of the initial kinetic energy, independent electron surface hopping simulations qualitatively agree with the experimental observation that nonadiabatic energy dissipation only occurs if the initial kinetic energy exceeds the bandgap of the surface.

A study on cross peaks in two-dimensional optical spectroscopy: Quantum cross-correlation functions and interplay with excitonic coupling

We present a comprehensive theoretical framework for simulating the two-dimensional (2D) optical spectra of molecular systems with complex-valued quantum frequency fluctuation cross-correlation functions (FXCFs). The FXCF contains information on the indirect interactions between two separate molecular excitations via coupling to common harmonic bath modes. We derive the complete set of third-order nonlinear optical response functions and systematically analyze their dynamic spectral features in the resulting 2D spectra. These include cross peaks and oscillating features, which appear only when the full complex-valued FXCF is used. If only the real-valued or “classical” FXCF is considered, the spectral signatures of the indirect interactions via coupling to the common modes do not manifest in the 2D spectra. In addition, we investigate how these spectral signatures of indirect interaction are modulated in the presence of excitonic coupling.

Amphiphilic Fluorinated Block Copolymer Additives for Ultrastable Aqueous Zn-Ion Batteries

Microscopic elasticity from MD. I. Bulk solid and fluid systems

Computational modeling, such as molecular dynamics and Monte Carlo simulations, can be used to estimate the elastic properties of materials through various stress and strain relationships. Here, we demonstrate the effectiveness of the stress–stress fluctuation (SSF) method to estimate the elastic properties of simple van der Waals and molecular materials. The SSF method allows computation of the complete elasticity tensor from a single equilibrium simulation without requiring any type of deformation. While extensively used to characterize the elastic coefficients of crystalline solids and glassy systems, application of the SSF method to fluid systems and biomaterials has been limited. Starting with argon in the solid, liquid, and gas phases, we show that the SSF method gives elastic coefficients and moduli in excellent agreement with values obtained with the explicit deformation and volume fluctuation methods. Comparison of the elastic coefficients and bulk modulus for solid argon with previous computational studies and experimental data provides further validation of our numerical implementation. Beyond argon, we show that the elastic properties of molecular fluids simulated with the coarse-grained MARTINI force-field, which include multi-body interactions such as angle potentials, are also accurately captured by the SSF method. Moreover, the impulsive correction for truncated potentials is essential to obtain accurate values for these fluids and vanishing shear moduli. Our results highlight the broad applicability of the SSF method across a broad range of systems and lay the foundation for its use to characterize the elastic properties of complex molecular systems.

Microscopic elasticity from MD. II. Liquid interfaces and lipid membranes

Lipid membranes not only play critical roles in many cellular functions but are also unique in that they have properties of both fluid and elastic materials. While 2D elasticity theories, such as Canham–Helfrich–Evans, adequately capture the dominant energetics of membrane deformation, a full characterization of the 3D elastic response is necessary to account for the many modes of deformation and the role that lipid structure plays in determining the elastic energy. We use the stress–stress fluctuation (SSF) method to obtain local elasticity profiles of a simple water–dodecane interface and a lipid membrane from coarse-grained MARTINI molecular dynamics simulations. We validate the results from the SSF method through the explicit deformation method, which measures the change in the local stress tensor relative to a specific strain. Furthermore, we show that some expected symmetries of the elasticity tensor are locally broken due to the lateral fluidity of the interfacial systems and the physical constraint of mechanical equilibrium. Profiles of the lateral and transverse shear moduli show that the membrane is locally fluid, while the transverse shear modulus is locally nonzero, but its integral vanishes. We define the area, Young’s, and bulk moduli, as well as the Poisson ratio for a lipid membrane through the compliance tensor, and use the area modulus to estimate the position of the neutral surface and the macroscopic bending modulus. Our elasticity calculations provide critical insights into the local mechanical properties of lipid bilayers and unravel the role of lateral fluidity in the membrane’s elastic response.