Browse Articles
Discover research articles across all indexed journals
Revealing structure–property relationships and charge transfer dynamics in host–guest phosphorescent organic light-emitting diodes
Host materials are widely employed in organic light-emitting diodes (OLEDs) to achieve a high external quantum efficiency, initially presumed to function solely through molecular motion restriction. Recent experiments suggest that the host matrix may also facilitate energy transfer processes, yet theoretical understanding remains limited. Here, we employ non-adiabatic molecular dynamics to investigate excited state dynamics in a host–guest system comprising 2,7-dibromophenanthrene-9,10-dione (27PNDO) as the emitter and 6,11-dibromodibenzo-[f,h]quinoxaline (27QNX) as the host material. Our simulations reveal that 27QNX enables phosphorescence of 27PNDO at room temperature, a phenomenon that is absent in 27PNDO films due to inefficient singlet-to-triplet conversion. The binary system establishes two phosphorescence pathways: direct intersystem crossing in 27PNDO and energy transfer from the S1 state of 27QNX to a higher-lying triplet state of 27PNDO, followed by relaxation to T1. Molecular flexibility strongly influences exciton dynamics, with excessive conformational freedom in the 27PNDO dimer inhibiting intersystem crossing. Furthermore, molecular packing geometry proves crucial: antiparallel configuration facilitates S1 → T2 → T1 conversion, while parallel configuration induces molecular distortions that impede triplet state population. These findings emphasize the importance of both emitter selection and host material design in the development of efficient phosphorescence materials.
Thermal transport anomalies of electrolyte solutions in the water supercooled regime: Signatures of the liquid–liquid water phase transition
Water exhibits remarkable anomalies when supercooled, attributed to a hypothesized liquid–liquid phase transition (LLPT) between low-density and high-density liquid (HDL) phases. Using non-equilibrium molecular dynamics simulations, we explore thermal transport and coupled effects in supercooled NaCl and LiCl solutions (1–4 m, 200–300 K). At 1 m, thermal conductivity exhibits a pronounced minimum near 220 K, coinciding with maxima in isothermal compressibility and minima in the speed of sound, both of which are signatures of critical fluctuations. The anomalies progressively diminish with increasing salt concentration and vanish at 4 m, suggesting suppression of the LLPT. The Soret coefficient exhibits striking behavior, which is initially thermophobic at high temperatures (>280 K, solute migrates toward the cold side), becomes thermophilic upon cooling (solute migrates toward the hot side), and then reverts to thermophobic below 220 K. This behavior correlates with structural changes in the hydrogen-bond network of water. In particular, we find that the deep minima in the Soret coefficient, corresponding to the strongest thermophilic response in NaCl and LiCl, occur in thermodynamic states characterized by a low fraction of HDL-like structures, indicating a predominance of highly tetrahedrally ordered water environments. Furthermore, Seebeck coefficients exhibit sign reversals near 220–230 K, highlighting the thermoelectric sensitivity to structural transformations and temperature. These findings establish thermal transport as a sensitive probe of supercooled water, revealing that electrolyte solutions preserve the water’s anomalies deep into the supercooled regime.
Dynamics and transport of Bose–Einstein condensates in bent potentials
The dynamics of bosons in curved geometries have recently attracted significant interest in quantum many-body physics. Leveraging recent experimental advances in tailored trapping landscapes, we investigate the quantum transport of weakly interacting bosons in two-dimensional bent trapping potentials, showing that geometry alone can serve as a precise control knob for tunneling dynamics. Using time-adaptive many-body simulations, complemented by mean-field analysis and exact diagonalization, we analyze both static and dynamical properties of bosons confined in the bent potential. We reveal how bending an initially straight channel induces a transition from density localization to delocalization and drives the buildup of correlations in the ground state. In the dynamics, the bend acts as a tunable barrier that enables controllable tunneling: weak curvature allows coherent tunneling across the bend, while a stronger bend suppresses transport and enhances self-trapping. The tunneling rate can be precisely tuned by geometric parameters, establishing bent traps as versatile platforms for geometry-controlled quantum transport.
Spectral decomposition of human BCL2 bonded to a PROTAC
In this study, we have decomposed the linear infrared spectra and two-dimensional infrared spectroscopy of a VHL-recruiting Proteolysis-targeting chimera (PROTAC) complex with BCL-2 to understand the spectral signatures of this complex. Our findings show that both VHL and BCL-2 units have distinct spectral signatures that contribute to the total spectra in different regions. Furthermore, we observed that the interaction between VHL and BCL-2 within the PROTAC complex leads to unique spectral features, indicating a strong synergistic effect. Through detailed analysis, specific bands were identified that correspond to the vibrational modes of the individual components, as well as their interactive modes within the complex. This study provides valuable insight into the molecular interactions within the PROTAC complex, offering a deeper understanding of its structure and function. These insights could be pivotal in designing more efficient PROTACs for targeted protein degradation in therapeutic applications.
Transfer-learning enhanced adaptive sampling for accelerating ultrafast spectroscopy
Ultrafast transient absorption (TA) spectroscopy is a versatile tool for probing photoinduced dynamics in complex materials, but it often requires dense temporal sampling and extensive signal averaging, resulting in lengthy data acquisition times. Here, we present a data-driven sampling method, called Transfer-Learning Enhanced Adaptive Sampling (TEAS), which significantly accelerates TA measurements by reducing the number of required time points while preserving the full spectral and temporal information content of the original data. TEAS combines transfer learning with adaptive sampling to exploit cross-wavelength patterns, concentrating measurements on the most informative regions for greater efficiency and accuracy. The method does not rely on any specific mathematical or kinetic model, making it a flexible and general framework for accelerating measurements across a wide range of spectroscopic modalities. We demonstrate that this method can accurately reconstruct TA data using less than 1% of the total experimental measurements under varying signal-to-noise conditions, consistently outperforming traditional approaches that lack transfer learning or adaptive sampling. These results highlight the potential of TEAS as a broadly applicable, cost-effective solution for speeding up ultrafast spectroscopy and enabling real-time, data-driven experimentation.
Shape anisotropy controls 2D melting pathway
The melting of two-dimensional systems is a fundamental challenge in condensed matter physics, where topological defects and thermal fluctuations play a key role. This work uses molecular dynamics simulations to investigate the melting of particles interacting via the Gay–Berne potential in the weak anisotropy regime (1.0 ≤ k ≤ 1.2). We demonstrate that the melting mechanism depends critically on the particle aspect ratio. For weak anisotropy (k < 1.15), the system follows a hybrid Bernard–Krauth scenario, featuring a continuous crystal-to-hexatic transition, followed by a first-order hexatic-to-isotropic liquid transition. At k ≥ 1.15, the system switches to the full Berezinskii–Kosterlitz–Thouless–Halperin–Nelson–Young scenario with two continuous Berezinskii–Kosterlitz–Thouless transitions. Introducing binary mixtures of particles with different anisotropies suppresses the first-order transition, stabilizing the continuous melting pathway. Therefore, weak shape anisotropy serves as a fundamental switching parameter governing the universal melting behavior of two-dimensional systems.
Optical pump-terahertz emission probe of ultrafast magnetization dynamics
Understanding spin dynamics on ultrafast timescales offers not only fundamental insights into the coupling of both electrons and phonons with spins but also opportunities for faster and more efficient spintronic devices. However, reliable access to ultrafast spin dynamics in materials and devices under realistic device-operation conditions remains a challenge. Here, we demonstrate a spectroscopic method of optical pump-terahertz (THz) emission (OPTE), which gives direct access to the ultrafast demagnetization and re-magnetization dynamics in a contact-free method under ambient conditions. The observation time window is not limited by the pulse width of THz radiation emitted by the sample. We measure the ultrafast spin dynamics in a laser-excited Fe monolayer. Our measurements disentangle distinct components originating from (i) the ultrafast magnetization quenching that occurs in less than 0.5 ps and (ii) the fast and slow magnetization recoveries that correspond to the spin–lattice coupling and heat diffusion from the sample into the substrate/surroundings, respectively. The OPTE can be a platform to probe and optimize the performance of magneto-optical recording materials and THz emission applications.
Triple excitations in nuclear–electronic orbital coupled cluster theory for multiple quantum protons
Within the nuclear–electronic orbital (NEO) framework, specified nuclei, typically protons, are treated quantum mechanically on the same level as the electrons. This framework allows for nuclear quantum effects, such as anharmonic zero-point energy, to be included in quantum chemical calculations in a computationally efficient manner. NEO coupled cluster (NEO-CC) methods provide a promising strategy for producing accurate ground-state properties of moderately sized molecular systems. Herein, the inclusion of triple excitations in NEO-CC methods is explored for systems with multiple quantum protons. Full and perturbative treatments of electron–electron–proton and electron–proton–proton triple excitations are investigated. The perturbative treatment agrees quantitatively with the full treatment for proton affinity calculations and is much more computationally efficient, especially for systems with multiple quantum protons. The NEO-CCSD(T) method, which includes single, double, and perturbative electron–electron–proton, electron–proton–proton, and electron–electron–electron triple excitations, reproduces experimentally measured proton affinities within experimental uncertainty using a complete basis set extrapolation. Moreover, application of the NEO-CCSD(T) method to protonated water tetramers, with all nine protons treated quantum mechanically, incorporates the essential anharmonic zero-point energy with only a single-point energy calculation. NEO-CC methods offer an accurate and computationally practical approach for inclusion of nuclear quantum effects in molecular systems and may serve as a benchmark for lower-level NEO methods.
Mixed Gaussian and plane wave basis set implementation of the random phase approximation and of <i>σ</i> -functionals within the program package CP2K
The reliability of the random phase approximation (RPA) and of σ-functional methods in conjunction with the mixed Gaussian and plane wave (GPW) basis set scheme as implemented in the CP2K package is investigated. First, based on the results for thermochemical properties of molecules and structural properties of crystalline solids, we establish reliable computational setups for practical calculations. Next, we compare the results obtained with these setups to those from standard GPW basis set approaches. For molecules, the results of RPA and σ-functional calculations within the GPW scheme are slightly worse, though still comparable, to those obtained using the standard Gaussian basis set scheme, provided a large enough orbital basis set is employed in the GPW calculations. Furthermore, the GPW calculations using σ-functionals are clearly more accurate than RPA calculations and even more so than those of conventional Kohn–Sham methods in the prediction of reaction energies and barrier heights for main group chemistry. For crystalline solids, the RPA and σ-functional methods significantly outperform the conventional Perdew–Burke–Ernzerhof (PBE) method in determining lattice constants. However, only the RPA method provides improved results for bulk moduli, while the σ-functional method yields errors comparable to those of the PBE method. A comparison of the results of the plane wave basis set calculations with the projector augmented wave method shows reasonable consistency for lattice constants and bulk moduli.
Effects of trap sites on magnetic-field dependent electric conductance and recombination of carriers photogenerated in a dye-doped organic semiconductor film device
Photogenerated radical ion pairs are important intermediates that govern the optoelectronic and magnetic responses of organic materials. We have succeeded in observing a singlet-born radical pair with a microsecond-order lifetime in a photoelectric device comprising a perylenediimide-doped poly(N-vinylcarbazole) film at room temperature. The simultaneously detected transient optical absorption signal due to the electron and photocurrent signal due to the hole are enhanced by an applied magnetic field of 250 mT, which is explained by the quantum spin dynamics of the radical pair. Detailed analysis of the magnetic field effect and its temperature dependence has revealed that the photogenerated holes that comprise the radical pair are captured in either a shallow trap site of a few meV depth or a deep trap site of 100–200 meV depth, from which detrapping-limited (∼100 ns) and tunneling recombination (a few microseconds) occur, respectively. In contrast to the nearly temperature-independent recombination dynamics, the hole drift mobility exhibits large activation energies of over 100 meV because the hole transport in the micrometer range is limited by detrapping from the deep trap site. The present study demonstrates the importance of trap sites in disordered materials, which can be utilized as reservoirs for long-lived radical pairs.
Influence of dipolar solvent fluctuations on polyelectrolyte thermodynamics and complex coacervation
We present a self-consistent polyelectrolyte field theory that reveals the impact of solvent polarity and polymer semiflexibility on polyelectrolyte solution thermodynamic behavior. Our approach incorporates a microscopic treatment of the solvent dipolar field and focuses on the importance of the charge separation distance in the dipole solvent. Consequently, this leads to an inhomogeneous dielectric medium at microscopic length scales and a significant free-energy contribution that manifests as the insolubility of uncharged species in a polar solvent. We then add the Born solvation energies of each charged species to account for their inherent solubility. Using this updated theory, which incorporates quadratic-order concentration fluctuation corrections, we generate phase diagrams for oppositely charged polyelectrolyte solutions that display phase re-entrant behavior for weakly charged polyelectrolytes and capture phase behavior consistent with recent experimental findings.
A data-driven and quantum chemistry-anchored framework for modeling and classifying carbon–lithium bonding in organolithium aggregates
We present a quantum chemistry-based, data-driven framework for the automated classification of carbon–lithium bonding motifs in archetypal organolithium aggregates. Starting from ab initio potential energy surfaces-guided sampling, we constructed a chemically complete dataset of 81 optimized gas-phase aggregates of methyllithium, t-butyllithium, and phenyllithium (600 C–Li bonds in total) spanning all relevant nuclearities and bonding modes. Twenty geometric, electronic, and topological descriptors obtained from quantum theory of atoms in molecules and Electron Localization Function (ELF) analyses were evaluated via correlation clustering, yielding a minimal, non-redundant, chemically meaningful set dominated by the ELF basin electron population and key bond-path metrics. This reduced descriptor set was used to train two complementary supervised models—a multi-task fully connected neural network and a bootstrap-aggregated decision tree—achieving accuracies of 84% (nucleophile type), 89% (aggregation state), and 84% (bond type) on validation data. Both methods consistently identified ELF-derived descriptors as the most discriminative, enabling physically grounded separation of bonding regimes (2c–2e, multi-center, non-classical, π–Li) and providing an interpretable, transferable platform for high-throughput bonding analysis in organometallic chemistry.
easyPARM v4.00: A Python-based tool for the automated parameterization of metalloproteins and metal-organic polyhedra with multiple metal centers
Force-field parameters for classical molecular dynamics simulations of metal centers are often derived from electronic structure calculations due to the inexistence of transferable libraries. Metalloproteins and metal-organic polyhedrons systems add more layers of complexity with respect to molecular transition metal complexes due to the usual presence of multiple metal cores and the coordination with amino acids of the protein and/or non-standard structures, forcing user intervention and making the parameterization process very tedious, time-demanding, and prone to errors. This work presents easyPARM v4.00, a Python-based tool that allows the automated parameterization of these (multi)metallic systems, strongly minimizing human intervention and computational cost. Additional implementations like compatibility with the GAMESS-US software and the non-interactive mode are explained in detail, whereas the quality of the obtained parameters is systematically validated against reference data (including density functional theory molecular dynamics), fully demonstrating that the proposed procedure is not only streamlined but also reliable and versatile. The code is distributed as open source and free of charge on GitHub at https://github.com/Abdelazim-Abdelgawwad/easyPARM.git.
Replicated liquid theory in 1 + <i>∞</i> dimensions
We develop a replicated liquid theory for structural glasses that exhibit spatial variation of physical quantities along one axis, say z-axis. The theory becomes exact with an infinite transverse dimension d − 1 → ∞. It provides an exact free-energy functional with a space-dependent glass order parameter Δab(z). As a first application of the scheme, we study diverging lengths associated with dynamic/static glass transitions of hard spheres with/without a confining cavity. The exponents agree with those obtained in previous studies on related mean-field models. Moreover, it predicts a non-trivial spatial profile of the glass order parameter Δab(z) within the cavity, which exhibits a scaling feature approaching the dynamical glass transition.
The effect of selective monodoping and co-doping at A/B-site on the ferroelectricity and piezoelectricity in KNbO3
Ion doping is one of the most effective strategies to tailor the piezoelectric properties of alkali niobate ceramics. However, its underlying mechanisms remain insufficiently understood. In this work, the structural, ferroelectric, and piezoelectric properties of the selected A- or B-site monodoping and codoping in orthorhombic KNbO3(KN) are studied by density-functional calculations. A-site substitutions include alkali (Li, Na, Rb, Cs), alkaline-earth (Mg, Ca, Sr, Ba), and Bi ions, while B-site doping involves Nb replacement with isovalent (V, Ta, P, As), group IVB (Ti, Zr, Hf), and Bi atoms. Two co-doping combinations, (Na, Sb) and (Ba, Zr), are also studied. The orientational averaged shear, transverse, and longitudinal piezoelectric coefficients d̄15*, d̄31*, and d̄33* of the A/B-site monodoping and codoping in KN piezoceramics are calculated from the results of single crystals. The calculated values clearly indicate that the substitution of Na, Cs, and Ca at the A-site can result in higher piezoelectricity, while the incorporation of V, Ta, Ti, Bi, and Sb to substitute Nb atoms induces better piezoelectric performance. Moreover, the codoping technique of (Na, Sb)- and (Ba, Zr)-doped KN crystals significantly enhances the piezoelectricity compared with the pure KN and those monodoping cases. These findings demonstrate that ion doping plays a critical role in flattening the energy landscape and enhancing the piezoelectric performance of perovskite ferroelectrics.
Hybrid explicit-droplet/implicit solvation model to accelerate constant-potential molecular dynamics simulations
Using hybrid solvation model has become an important way to simulate the dynamics of electrochemical solid–liquid interfaces under realistic solvation and potential. However, since it typically relies on fully covering explicit solvent layers, it suffers from high computational cost and the dissolution of solvent molecules into the implicit solvent. To address these challenges, we present a hybrid explicit-droplet/implicit solvation model implemented based on VASPsol++, which enables efficient constant-potential molecular dynamics simulations around local reactive sites. This model employs an algorithm to exclude implicit solvent within the droplet and a velocity-reflection algorithm that prevents explicit solvent molecules from dissolving into the implicit solvent. It features both radius- and density-constant implementations and integrates a continuous cavity. Validated with established water-layer models, the droplet approach reliably replicates key interfacial properties, such as electron-count fluctuations and free-energy barriers from enhanced sampling calculations, in exemplar systems including Co–N–C motifs and MoS2 edges. Notably, this model accelerates barrier-calculation speed by 2–4 times, depending on slab size and specific settings, while providing reliable results. This study offers a new tool through which simulating the electrochemical interface using constant-potential molecular dynamics is significantly accelerated and more broadly accessible.
Tensorial spin-phonon relaxation reveals mode-selective relaxation pathways in a single-molecule qubit
Understanding and controlling spin relaxation in molecular qubits is essential for developing chemically tunable quantum information platforms. We present a first-principles-parametrized analytical framework for evaluating spin relaxation dynamics in vanadyl phthalocyanine (VOPc) and its oxygenated derivative, VOPc(OH)8. By expanding the spin Hamiltonian in vibrational normal modes and computing both linear and quadratic spin–phonon coupling tensors via finite differences of the g-tensor, we construct a relaxation tensor that enters a Lindblad-type master equation, capturing both direct (one-phonon) and Raman (two-phonon) processes. A mode-resolved analysis reveals that relaxation is funneled through only a handful of low-frequency vibrations: in VOPc, three out-of-plane distortions of the phthalocyanine ring and V–O unit dominate, whereas in VOPc(OH)8, the additional oxygens shift these modes downward and suppress two of them, leaving a single strongly coupled mode as the main decoherence pathway. Both longitudinal (T1) and transverse (T2) relaxation are governed by this same set of vibrational modes, indicating that coherence loss is controlled by a common microscopic mechanism. This mode-selective picture offers a design strategy for engineering longer-lived molecular qubits.
Resonances in inelastic collisions of Ne + D2 in the cold energy regime
Scattering resonances are quantum phenomena arising from the decay of metastable collision complexes trapped by a centrifugal barrier or supported by a closed channel that is coupled to a scattering state. As such, resonances can provide significant insights into the scattering process and serve as a sensitive probe of the interaction potential. In this article, we present a detailed analysis of a cluster of shape resonances associated with the orbital angular momentum L = 5 in the j = 2 → j′ = 0 rotational transition in Ne + D2 collisions for vibrational levels v = 0, 1, and 4. The energies and lifetimes of the resonances arising from different values of the total angular momentum quantum number J were analyzed through numerical fitting of the scattering matrix and employing a one-dimensional model based on an effective potential. We further investigated the sensitivity of the resonances to changes in the alignment of the D2 internuclear axis with respect to the initial relative velocity. Our results show that resonances can be exquisitely controlled by carefully selecting the initial alignment of the D2 molecule. In particular, not only the intensity of the resonance can be modulated but also the shape of the overall resonance profile can be altered, depending on the stereodynamical preferences of the individual resonances that contribute to the cluster.
THz insight into Debye relaxation in liquid water: Link to self-diffusion and viscosity
A non-standard analysis of the dielectric loss spectrum of liquid water in the Debye relaxation region (108–1013 Hz) is carried out in terms of dynamic conductivity σ(ν), with the Debye dielectric loss dome represented as the spectral trapezoid of an overdamped Lorentzian oscillator. Debye relaxation, in this framework, reflects the low-frequency tail of a strongly overdamped molecular oscillatory process with a characteristic frequency around 0.3 THz. The effectiveness of the σ-approach for identifying the relationship between the dielectric response and the self-diffusion D and viscosity η coefficients of liquid water is shown. Analytical expressions that link the dielectric and transport parameters of liquid water over a wide temperature range, from the triple point to the critical point (273–647 K), are derived.
Topology and spectral entanglement in cavity-mediated photon scattering
We develop a microscopic diagrammatic theory for cavity-mediated photon scattering in a topological one-dimensional insulator described by the Su–Schrieffer–Heeger model. Within the velocity-gauge formulation, we derive the photon self-energy and vertex corrections arising from virtual electron–hole excitations coupled to a quantized cavity mode, and we evaluate the resulting polariton dispersion and two-photon correlation spectra. Our analysis shows that vacuum fluctuations of the cavity field induce a momentum-resolved self-energy that mixes conduction and valence bands through virtual photon exchange, producing interband hybridization and avoided crossings in the electronic dispersion. This “cavity dressing” is symmetry-dependent, vanishing at the Brillouin-zone edge where the dipole matrix element is zero, and its strength is controlled by the spatial coherence range ζ≈(lc/a)2 of virtual excitations. We further examine how the cavity modifies nonlinear optical observables, including the Kerr nonlinearity and biphoton spectral entanglement, and identify the regimes where these effects become sensitive to the underlying topological phase. The theoretical framework established here provides a unified description of light–matter coupling in topological and polaritonic systems, bridging solid-state cavity QED with the emerging field of cavity-modified quantum materials. Our results suggest that engineered photonic environments can coherently reshape the electronic landscape of topological insulators, offering new routes to control collective electronic and optical phenomena through vacuum-field fluctuations.