Journal of Chemical Physics最新文献

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.

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.

Electromagnetic response is commonly computed in two languages: length-gauge molecular polarizabilities and velocity-gauge (Kubo) conductivities for periodic solids. We introduce a compact, gauge-invariant bridge that carries the same microscopic inputs-transition dipoles and interaction kernels-from molecules to crystals and heterogeneous media, with explicit SI prefactors and fine-structure scaling via αfs. The long-wavelength limit is handled through a reduced dielectric matrix that retains local-field mixing; interfaces and 2D layers are treated with sheet boundary conditions (rather than naïve ultrathin films); and length-velocity equivalence is enforced in practice by including the equal-time (diamagnetic/contact) term alongside the paramagnetic current. Finite temperature is addressed on the Matsubara axis with numerically stable real-axis evaluation (complex polarization propagator), preserving unit consistency end-to-end. The framework enables predictive, unit-faithful observables from radio frequency to ultraviolet-RF/microwave heating and penetration depth, dielectric-logging contrast, interfacial optics of thin films and 2D sheets, and adsorption metrics via imaginary-axis polarizabilities. Numerical checks (gauge overlay and optical f-sum saturation) validate the implementation. Immediate priorities include compact, temperature- and salinity-aware kernels with quantified uncertainties and operando interfacial diagnostics for integration into multiphysics digital twins.

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.

The possibility of a liquid-liquid transition (LLT) in supercooled water has sparked decades of debate. Recent pump-probe experiments interpret two peaks in the structure factor S(q) during and after decompression of high-density liquid (HDL) as evidence of coexistence with low-density liquid (LDL). However, this interpretation presents a fundamental puzzle: such coexistence is implausible at ambient pressure, below the estimated location of the liquid-liquid critical point (LLCP). Here, we use decompression simulations with ML-BOP to reconcile this contradiction. Even when water decompresses along the LLT, S(q) retains a single peak because HDL and LDL domains remain nanoscopic. We explain the two-peak S(q) observed experimentally as a single evolving liquid peak superimposed on a slower to respond, colder HDL arising from the temperature gradient across the sample. The simulations reveal that the decisive LLT signature is a transient growth and decay of the apparent correlation length ξ at low q, which emerges only when decompression proceeds along the LLT, with maximum ξ near the LLCP. Importantly, ξ remains low when decompressing from T ≥ Tc, or too rapidly. The experimental signatures could be explained by an exponential pressure drop to the LLT in ∼10 ns, the growth of ξ as LDL domains develop, peaking near the LLCP at ∼50 ns, and subsequent entry into the single-phase regime, from which crystallization proceeds. Our findings resolve the contradiction between the LLCP location and structural signatures, identifying the low q region of S(q) evolution-not peak splitting-as the key structural marker of the LLT in water.

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.

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.

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.

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.

We investigate strategies for simulating open quantum systems coupled to dissipative baths by comparing explicit wave function-based discretization [via multi-layer multi-configuration time-dependent Hartree (ML-MCTDH)] and the implicit density matrix-based master equation method [via tree tensor network hierarchical equations of motion (TTN-HEOM)]. For dissipative baths characterized by exponentially decaying bath correlation functions, the implicit discretization approach of HEOM-rooted in bath correlation function decompositions-proves significantly more efficient than explicit discretization of the bath into discrete harmonic modes. Explicit methods, like ML-MCTDH, require extensive mode discretization to approximate continuum baths, leading to computational bottlenecks. Case studies for two-level systems and a Fenna-Matthews-Olson complex model highlight TTN-HEOM's superiority in capturing dissipative dynamics with relaxations with a minimal number of auxiliary modes, while the explicit methods are as exact as the HEOM in pure dephasing regimes. This comparison is enabled by the TENSO package, which has both ML-MCTDH and TTN-HEOM implemented using the same computational structure and propagation strategy.