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How well do classical and multiscale QM/MM molecular dynamics simulations capture stereoelectronic effects? A comparative study on atropisomerism
Subtle stereoelectronic effects can play an important role in drug discovery and other application areas, with atropisomerism gaining increasing interest recently. This raises the question of which level of theory is required to model such phenomena accurately by computational means, i.e., are classical mechanics (MM) with a fixed-charge force field sufficient or is a quantum-mechanical (QM) treatment needed? Here, the ability of classical and multiscale (QM/MM) molecular dynamics simulations to capture these effects is assessed by calculating free-energy differences between the conformational states of a series of molecular balances. Significantly different free-energy profiles are obtained, and the differences are rationalized via a detailed geometric characterization and force-field investigation, pointing toward limitations of the classical approximations. Interestingly, despite these differences, the calculated free-energy differences are within chemical accuracy for all considered methods, highlighting the power of error compensation and the need to check the underlying raw data whenever possible.
Detection of hexagonal fluid crystalline phase in polymer suspensions as suggested by de Gennes via anomalous small-angle x-ray scattering II. Continuation-melting of the liquid crystalline phase as observed in semi-dilute solutions of polyacrylate macroions with concentrations of 55 and 110 mM surrounded by thallium counterions
Element specific scattering techniques known as anomalous small-angle x-ray scattering have been employed in the analysis of the thallium counterion distribution in aqueous polyacrylate solutions of concentrations 25, 55, and 110 mM. The three basic scattering functions—pure-resonant, mixed-resonant, and non-resonant—–have been deduced explicitly, thereby revealing decisive structural and quantitative information of the involved chemical components. In continuation of a previous paper, at a molar concentration of 55 mM, a hexagonal lattice structure of cylinders with an axis of h = 5.3 nm and a lattice parameter α0 = 8.4 nm was identified, with about 87% of the Tl+-ions located in the cylinders. From the Lindemann criterion, the stability of the hexagonal phase is deduced. At a concentration of 110 mM, a strong disordering of the hexagonal phase is observed, and only residuals of the Bragg reflections are detected with h = 7.6 nm and α0 = 14.5 nm, which can be interpreted as melting of the hexagonal phase, the latter being confirmed by the Lindemann criterion.
Linear tuning of exciton binding energy in colloidal quantum dot solid-state film
Colloidal quantum dot (QD) solid-state films are fundamental building blocks for modern optoelectronic devices. In these films, the complex dielectric environment formed by surrounding QDs and organic ligands significantly modifies their electronic and excitonic properties, posing a considerable theoretical challenge. Herein, we report a robust first-principles scheme capable of accurately predicting the fundamental and optical gaps of these films. The methodology’s success is rooted in a twofold innovation: the development of optimized, dimensionally consistent Gaussian basis sets that accurately treat both extended and confined systems, and a unique density functional parameterization. This parameterization employs screened range-separated hybrid density functional theory, uniquely incorporating the QD size-dependence of the range-separation parameter while introducing the solid-state film’s scalar dielectric constant. This comprehensive scheme determines the electronic structure with an accuracy competing with state-of-the-art self-consistent GW calculations. Applying it to group IV and II–VI QD solid-state films, we achieve an excellent reproduction of experimental fundamental and optical gaps, allowing the accurate determination of the exciton binding energy. We established that this binding energy in solid-state films scales linearly with the inverse QD diameter, a key relationship predicted by classical electrostatics that is largely independent of the material type. Conventional hybrid functional calculations are found to severely fail to quantify this energy and its size-dependent scaling relations. This work provides a cost-effective and broadly applicable theoretical framework for accurately determining the electronic and optical properties of colloidal QD solid-state films.
Third and fourth density and acoustic virial coefficients of neon from first-principles calculations
The third and fourth density and acoustic virial coefficients of neon were determined at temperatures between 10 and 5000 K from first principles employing the path-integral Monte Carlo (PIMC) approach. For these calculations, we used the pair potential of Hellmann et al. [J. Chem. Phys. 154, 164304 (2021)], which is based on supermolecular ab initio calculations with basis sets of up to octuple-zeta quality and levels of theory up to coupled cluster with single, double, triple, quadruple, and perturbative pentuple excitations [CCSDTQ(P)]. The potential also accounts for relativistic, retardation, and post-Born–Oppenheimer effects and is provided with reliable uncertainty estimates. To incorporate nonadditive interactions, we developed a nonadditive three-body potential based on extensive supermolecular CCSD(T), CCSDT, and CCSDT(Q) calculations with basis sets of up to sextuple-zeta quality. This potential also accounts for relativistic effects. The very small nonadditive four-body contributions to the fourth virial coefficients were considered using a relatively simple nonadditive four-body potential based on supermolecular CCSD(T) calculations. We calculated the third and fourth density and third acoustic virial coefficients directly by PIMC and the fourth acoustic virial coefficient indirectly using thermodynamic relations between the density and acoustic virial coefficients. The uncertainties of the pair potential and those estimated for our nonadditive three-body potential were rigorously propagated in the PIMC calculations into uncertainties for the virial coefficients. These uncertainties are distinctly smaller than those of almost all of the corresponding experimental virial coefficient data.
Anion photoelectron spectroscopy of the hydrogen iodide anion, HI−
Among the hydrohalic acids, only hydrogen iodide (HI) forms its parent anion. HI− was identified mass spectrometrically, having been seen in three different anion-forming environments. In this work, HI−/DI− anions were produced by Rydberg electron transfer using electronically excited K**(8d) atoms as HI/DI collision partners, after which their anion photoelectron spectra (aPES) were measured using both magnetic bottle and velocity map imaging electron energy analyzers. The electron affinities (EA) of HI and DI were determined to be EA(HI) = 0.051 ± 0.015 eV and EA(DI) = 0.028 ± 0.020 eV, while the bond dissociation energies (D0) of their respective anions were determined to be D0(HI−) = 0.045 ± 0.015 eV and D0(DI−) = 0.063 ± 0.020 eV. Analysis of the vibrational structure in their aPES revealed that these anions possess double-well potentials, with their vibrational wavefunctions ranging over the two wells via tunneling. Franck–Condon analysis identified the bond lengths at the two minima of the double-well potential to be ∼2.03 and ∼2.37 Å. Thus, HI− and DI− each exist in two forms. In addition to these valence-bound HI− and DI− anions, the existence of non-valence-bound HI− (and perhaps DI−) species was implied by weak but persistent shoulder-like photoelectron signals at extremely low electron binding energies. Comparison of the anion photoelectron spectrum of HI− with those of alkali halide anions, MX−, supported the covalent character of the H–I chemical bond.
Predicting random close packing of binary hard-disk mixtures via third-virial-based parameters
We propose a simple and accurate approach to estimate the random close packing (RCP) fraction of binary hard-disk mixtures. By introducing a parameter based on the mixture’s reduced third virial coefficient—which effectively captures three-body correlations and excluded-area constraints—we show that the RCP fraction depends nearly linearly on this parameter, leading to a near-universal collapse of simulation data over a wide range of size ratios and compositions. Comparisons with previous models by Brouwers and Zaccone indicate that the present approach provides more accurate and consistent predictions. The method can be naturally extended to polydisperse mixtures with continuous size distributions and is structurally consistent with the surplus equation-of-state formulation, offering a compact framework for understanding the near universality of RCP in hard-disk systems.
An investigation into low-lying electronic states of CH3S2 via threshold photoelectron imaging
Threshold photoelectron imaging of CH3S2− was performed, providing the electronic spectroscopy information of the CH3S2 radical. This allows for the accurate determination of the electron affinity of CH3S2 (EA = 1.757 ± 0.002 eV) and the term energy of the first vibrational excited state (T0 = 1.037 ± 0.005 eV) to be directly determined from the experimental spectra. The vibrational characteristics were assigned mainly to the S–S stretching mode in the ground state (X2A″), as well as the S–S–C bending mode in the first excited state (12A′) in conjunction with Franck–Condon simulations. The photoelectron angular distributions indicate that the photodetachment process predominantly involves two different molecular orbitals of CH3S2−. In addition, angular filtering photoelectron spectra were employed to further support the assignment of the spectral bands.
Charge transfer dynamics of the Ar+(2P3/2) + N2 reaction at very low collision energies
The charge transfer reaction Ar+ + N2 → Ar + N2+ has been studied for collision energies of 40, 90, and 170 meV with product energy and angle-differential crossed-beam velocity map imaging. Resonant multi-photon ionization was employed to create the charged reactant Ar+ in the 2P3/2 spin–orbit ground state with high purity. At the lowest studied collision energy of 40 meV, we could observe the N2+ product in the v = 0 vibrational level with a high amount of rotational excitation. This level is strongly dynamically suppressed at higher collision energies, where excited vibrational levels become accessible. In addition, a higher fraction of backward scattering is observed at this low collision energy compared to higher collision energies. This shows that the reaction dynamics of the charge-transfer reaction undergo a profound change from direct to unusual complex-mediated charge transfer dynamics at very low collision energy.
Thermoresponsivity and cononsolvency of a minimal polymer model in mixed solvents
We present computer simulations of a minimal polymer model in water–methanol mixed solvents that captures key features of the cononsolvency behavior of amphiphilic polymers in alcohol–water mixtures. Our results indicate that the effective interactions between polymer segments vary nonmonotonically with the water–methanol composition. Their temperature dependence, however, shows a transition from good-to-poor solvent conditions only in the aqueous, low-methanol regime, up to the solvent composition X* corresponding to the minimum of the lower critical solution temperature. Consistent with this, the polymer radius of gyration decreases sharply with increasing temperature for X < X*. This temperature sensitivity, however, disappears at X = X*, even though the temperature dependence of effective segmental interactions still indicates a good-to-poor solvent transition. This loss of thermoresponsivity, in agreement with previous experimental observations, arises from preferential methanol adsorption, which reduces the role of hydrophobic hydration and leads to a vanishing heat of polymer collapse. Finally, we highlight the role of mixing entropy, arising from methanol–water mixing during polymer collapse, in driving the cononsolvency effect at a fixed temperature.
Multi-parametric interferometric reflectance imaging sensor
Response of a ODT monolayer to rapid heating studied by vibrational sum frequency spectroscopy
A self-assembled monolayer of octadecanethiol adsorbed on a thin film of Au was flash-heated by illuminating the structure, further consisting of a glass substrate and a Ti contact layer, with a 19 ps laser pulse of 532 nm light from the backside, inducing a temperature increase by 113 K within 100 ps. The details of the temporal evolution of the temperature can be well modeled when taking into account the predominant light absorption in the Ti layer and the large thermal boundary resistance between the layers. The evolution of the molecular structure is time-resolved by vibrational sum frequency spectroscopy. While the molecules are initially tilted by 30° with respect to the surface normal, this order is rapidly lost, whereby the disordering lags 150 ps behind the temperature evolution. After 400 ps, the molecular order is dissolved.
Identification, comparison of genetic diversity, heat tolerance, and growth performance among Micropterus salmoides salmoides, Micropterus salmoides floridanus, and their reciprocal hybrids
A length-gauge origin-invariant approach to vibrational circular dichroism spectra without gauge-including atomic orbitals
We have extended the origin-invariant length gauge [LG(OI)] approach—originally developed by Caricato and co-workers for optical rotation (OR) and electronic circular dichroism (ECD)—to vibrational circular dichroism (VCD). This approach avoids the need for gauge-including atomic orbitals (GIAOs), which are typically required to circumvent the unphysical dependence of the CD rotatory strengths on the arbitrary choice of coordinate origin for length gauge (LG) computations. Benchmark VCD spectra are presented for (P)-hydrogen peroxide, (S)-methyloxirane, (1R, 5R)-α-pinene, and (1R, 4R)-camphor using Hartree–Fock (HF) theory and density functional theory (DFT) methods across a range of basis sets and compared to those obtained from LG, velocity-gauge (VG), and GIAO computations. These analyses show that for VCD, the LG(OI) approach does not converge to the basis-set limit as rapidly as the GIAO approach, but does yield similar quality spectra as GIAO for all major VCD peaks for quadruple-zeta-quality basis sets. The LG(OI) and VG VCD spectra are less reliable compared to GIAOs for smaller basis sets.
Research on overdyeing process of indigo and turmeric on nylon knitted fabrics
Diffusion in rugged energy landscapes in the presence of spatial correlations: A surprising route to Zwanzig’s mean-field prediction
Diffusion in rugged free-energy landscapes is central to diverse problems in chemical physics, biomolecular dynamics, polymer transport, and numerous disordered systems. Zwanzig’s well-known classic mean-field theory predicts that roughness reduces the diffusion coefficient by an exponential factor determined solely by the variance of the disorder. The numerical studies of Banerjee, Biswas, Seki, and Bagchi (BBSB) showed that this result fails for uncorrelated Gaussian-distributed site energies because rare but deep three-site traps dominate long-time transport. BBSB introduced Gaussian spatial correlations—originally developed in astrophysics to model turbulent density fluctuations—and demonstrated that even modest correlations suppress these pathological traps and restore Zwanzig’s exponential scaling. Here, we present a unified theoretical framework clarifying (i) why Zwanzig’s local averaging, which may be viewed as a Gaussian cumulant expansion, can break down, particularly due to uncorrelated disorder; (ii) how Gaussian spatial correlations reshape roughness increments, eliminate asymmetric multi-site traps, and thereby recover mean-field diffusion; and (iii) a derivation showing exactly how Gaussian spatial correlations modify roughness increments, trap statistics, and, ultimately, the diffusion constant. We also provide explicit numerical triplet examples illustrating the dramatic reduction of escape times produced by spatial correlations.
Trachoma prevention practice and associated factors among mothers having children aged 1–9 years in Debre Markos Town, Northwestern Ethiopia, 2024
Determining fluid–crystal phase boundaries for a binary hard-sphere mixture using direct-coexistence simulations
Determining fluid–crystal phase boundaries via direct-coexistence methods can be challenging due to the fact that the simulation box can introduce crystal strain. Recently, a direct-coexistence approach was developed, which allows one to easily identify the equilibrium strain-free fluid–crystal coexistence in monodisperse systems. Here, we show that this approach can be readily extended to binary mixtures forming stoichiometric binary crystals, allowing accurate and efficient determination of the phase boundaries. Moreover, we examine how the choice of the crystal plane in contact with the fluid affects the accuracy of the phase boundary determination. The method is easy to implement and does not require prior knowledge of the binary fluid’s equation of state. These results further establish the method as a robust and practical tool for accurately determining fluid–crystal phase boundaries.
Comparison of all-cause mortality risk factors in a population-based cohort study
Abstract All-cause mortality is a population health indicator of the combined impact of biological, behavioral, social, and healthcare-related factors. We used data from 3,803 participants (1,947 women, 51.2%; aged 20 to 81 years) of the population-based Study of Health in Pomerania (SHIP-START-0, 1997–2001), with a median follow-up duration of 20.2 years. Sex-stratified cox proportional hazard models were used to estimate associations between socioeconomic, lifestyle, anthropometric, and cardiovascular risk factors with all-cause mortality. During the 70,982 person-years, 1,029 deaths (641 men and 388 women) were determined as all-cause mortality. In men, type 2 diabetes (hazard ratio [HR] = 1.83 [95% confidence interval {CI}: 1.48 to 2.25; p < 0.001]), living without a partner (HR = 1.78 [95% CI: 1.41 to 2.24; p < 0.001]), being a current smoker (HR = 1.76 [95% CI: 1.41 to 2.20; p < 0.001]), older age (HR per year = 1.10 [95% CI: 1.10 to 1.11; p < 0.001]) and elevated hs-CRP (HR per mmol/l = 1.07 [95% CI: 1.03 to 1.11; p < 0.001]) where significantly associated with increased all-cause mortality. In women, just type 2 diabetes (HR = 1.70 [95% CI: 1.28 to 2.15; p < 0.001]) and elevated hs-CRP (HR per mmol/l = 1.07 [95% CI: 1.03 to 1.12; p < 0.001]) where significantly associated with increased all-cause mortality. Type 2 diabetes and inflammation were linked to higher all-cause mortality in both sexes, whereas being without a partner, current smoking, and older age were significant risk factors specifically for men.
Unveiling state-specific total-exchange dynamics in high-temperature N2–N2/N2–O2 collisions via QCT and neural-network modeling
State-specific molecular–molecular exchange (total-exchange) reactions are pivotal microscopic processes governing vibrational energy redistribution and dissociation kinetics in high-temperature non-equilibrium gases. Quasi-classical trajectory (QCT) calculations are performed to elucidate the competition among dissociation and exchange channels in N2(v1) + N2(v2) and N2(v) + O2(w) collisions. The results reveal that under low vibrational excitation (v ≤ 20), total-exchange emerges as the dominant reaction pathway in N2–N2 collisions, surpassing all dissociation channels. In the N2–O2 system, although total-exchange is generally a secondary pathway, its contribution can surpass that of the typically dominant O2-dissoc when highly excited N2 collides with ground-state O2. Notably, in both systems, the total-exchange cross section increases monotonically with total collision energy below the double-dissociation threshold, and its high-temperature rate coefficients are comparable to those of non-reactive vibration–vibration and vibration–translation (VV/VT) energy transfer, underscoring its critical role in driving multi-quantum vibrational transitions. To enable efficient large-scale prediction, we develop two neural-network models (N4-NN, N2O2-NN) trained on the QCT data that achieve excellent accuracy (R2 &gt; 0.99) with ∼91% lower computational cost. The predicted cross sections are fitted to a compact analytical form, yielding a parameterized database ready for engineering applications. This study elucidates the state-specific mechanism of total-exchange-controlled energy transfer and its energy-dependent evolution, providing a comprehensive data foundation for modeling high-temperature non-equilibrium flows.