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Controlling the size distribution in the nucleation of copper particles is crucial for achieving nanocrystals with desired physical and chemical properties. However, their synthesis involves a complex system of solvents, ligands, and copper precursors with intertwining effects on the size of the nanoclusters. We combine molecular dynamics simulations and density functional theory calculations to provide insights into the nucleation mechanism in the presence of a triphenyl phosphite ligand. We identify the crucial role of the strength of the metal–phosphine interaction in inhibiting the cluster's growth. We demonstrate computationally several practical routes to fine-tune the interaction strength by modifying the side groups of the additive. Our work provides molecular insights into the complex nucleation process of protected copper nanocrystals, which can assist in controlling their size distribution and, eventually, their morphology. [ABSTRACT FROM AUTHOR]

Recently, LiGa 5 O 8 was claimed to be a p -type dopable ultrawide-bandgap oxide, based on measurements of undoped material. Here, the electronic properties of potential acceptor dopant impurities in LiGa 5 O 8 are calculated using hybrid density functional theory to evaluate their potential for causing p -type conductivity. As with the related compound LiGaO 2 , the heavy oxygen-derived valence bands lead to stable self-trapped holes in LiGa 5 O 8. Acceptor defects and dopants also bind trapped holes (or small polarons), which lead to large acceptor ionization energies. The calculations here indicate that neither native acceptor defects (such as cation vacancies or antisites) nor impurity dopants can give rise to p -type conductivity in LiGa 5 O 8. Optical transitions associated with these defects are also calculated, in order to allow for possible experimental verification of their behavior. [ABSTRACT FROM AUTHOR]

Molecular dynamics and density functional theory simulations are used to predict the lattice and electronic contributions of thermophysical properties for UN, PuN, and mixed (U,Pu)N systems. The properties predicted include the lattice parameter, linear thermal expansion, enthalpy, and specific heat capacity, as a function of temperature. The simulation predictions for high temperature specific heat capacity are compared against experimental measurements to understand the behavior, and why differences in the experimental measurements are observed. The influence of adding U vacancies, N interstitials, and Pu to UN is also examined. For this, a new PuN potential parameter set is developed and used with the Kocevski UN potential, enabling the dynamics of mixed (U,Pu)N systems to be studied. How defects impact the thermophysical properties is important for understanding fuel behavior under different reactor conditions, and these mechanistic predictions can be used to support fuel performance codes where data is scarce. [ABSTRACT FROM AUTHOR]

Recently, LiGa 5 O 8 was claimed to be a p -type dopable ultrawide-bandgap oxide, based on measurements of undoped material. Here, the electronic properties of potential acceptor dopant impurities in LiGa 5 O 8 are calculated using hybrid density functional theory to evaluate their potential for causing p -type conductivity. As with the related compound LiGaO 2 , the heavy oxygen-derived valence bands lead to stable self-trapped holes in LiGa 5 O 8. Acceptor defects and dopants also bind trapped holes (or small polarons), which lead to large acceptor ionization energies. The calculations here indicate that neither native acceptor defects (such as cation vacancies or antisites) nor impurity dopants can give rise to p -type conductivity in LiGa 5 O 8. Optical transitions associated with these defects are also calculated, in order to allow for possible experimental verification of their behavior. [ABSTRACT FROM AUTHOR]

The orthorhombic phase of FeNbO4, a promising anode material for solid oxide fuel cells (SOFCs), exhibits good catalytic activity toward hydrogen oxidation. However, the low electronic conductivity of the material specifically in the pure structure without defects or dopants limits its practical applications as an SOFC anode. In this study, we have employed density functional theory (DFT + U) calculations to explore the bulk and electronic properties of two types of doped structures, Fe0.9375A0.0625NbO4 and FeNb0.9375B0.0625O4 (A, B = Ti, V, Cr, Mn, Co, Ni) and the oxygen-deficient structures Fe0.9375A0.0625NbO3.9375 and FeNb0.9375B0.0625O3.9375, where the dopant is positioned in the first nearest neighbor site to the oxygen vacancy. Our DFT simulations have revealed that doping in the Fe sites is energetically favorable compared to doping in the Nb site, resulting in significant volume expansion. The doping process generally requires less energy when the O-vacancy is surrounded by one Fe and two Nb ions. The simulated projected density of states of the oxygen-deficient structures indicates that doping in the Fe site, particularly with Ti and V, considerably narrows the bandgap to ∼0.5 eV, whereas doping with Co at the Nb sites generates acceptor levels close to 0 eV. Both doping schemes, therefore, enhance electron conduction during SOFC operation. [ABSTRACT FROM AUTHOR]

Identifying the oxidation structure of two-dimensional interfaces is crucial to improve surface chemistry and electronic properties. Beyond graphene with only phenyl rings, a novel carbon-nitrogen material, C3N, presents an intrinsic heterogeneous surface morphology where each phenyl ring is encircled by six nitrogen atoms, yet its atomistic oxidation structure remains unclear. Here, combining a series of density functional theory calculations and ab initio molecular dynamics simulations, we demonstrate that thermodynamically favorable oxidation loci are confined to the phenyl ring, and kinetic transformations of oxidation structures are feasible along the phenyl ring, whereas those toward nitrogen atoms are proven to be extremely difficult. These results are attributed to the lower barrier of oxygen atom migration along the phenyl ring, while the significantly high barriers toward nitrogen atoms are due to the heterogeneous potential energy surface for oxygen–C3N interaction. This work highlights the significance of surface morphology on the characteristics of oxidation structure, offering insights into tunable electronic properties via confined interfacial oxidation. [ABSTRACT FROM AUTHOR]

The photochromic behavior of the fulgide molecule relies on ring-closure and ring-opening processes involving conical intersections during excited state transformation between isomers. The precise location and topography of these conical intersections significantly shape the decay process and fluorescence phenomena inherent to the molecule. This work combines electronic structure theory calculations using the density functional theory and wavefunction methods, as well as surface hopping simulation to analyze the photochemical behavior of an experimentally synthesized fulgide molecule, (E)-p-methylacetophenylisopropylidenesuccinic anhydride (1E). Our study reveals the conical intersection between the first excited state (S1) and the ground electronic state (S0), which emerges beyond the S1 minimum of 1E to the ring-closing side. The distinctive topography of this conical intersection appears to be sloped. These findings suggest a reduced quantum yield for the formation of the closed isomer, indicating a higher likelihood of reformation of the open isomer(s). The surface hopping simulation further supports this observation, revealing a mere ∼8% quantum yield for the formation of the closed isomer. In addition, the photoisomerization of the fulgide molecule initiates a cascade of conduction switching and holds great potential for applications in molecular electronics. Delving into the realm of molecular electronics, we have further examined the electron transport properties, disclosing the higher conductivity of the closed isomer. [ABSTRACT FROM AUTHOR]

The conformational space of cis-1,2-cyclohexanediol, a model molecule for cyclic vicinal diols, was investigated using rotational spectroscopy and density functional theory calculations. Four low energy conformers within an energy window of 5 kJ mol−1 were identified computationally. A rotational spectrum of jet-cooled cis-1,2-cyclohexanediol was recorded with a chirped pulse Fourier transform microwave spectrometer. Two sets of rotational transitions were observed and could be assigned to conformers of cis-1,2-cyclohexanediol. The non-observation of other low energy conformers was explained by conformational conversion barrier height calculations and results from experimental spectra recorded with different carrier gases. Eight isotopologues, including those with 13C and 18O, of the lowest energy conformer were observed, allowing the determination of the semi-experimental equilibrium structure, reSE. Interestingly, the structural analysis revealed that the C–O bond length of the intramolecular hydrogen-bond donor is shorter than that of the acceptor. This appears to be a general characteristic of vicinal diols and can be used as a novel hydrogen-bond marker in such compounds. [ABSTRACT FROM AUTHOR]

In this work, the ultrafast intramolecular rotation behavior of 1,1,2,3,4,5-hexaphenylsilole has been investigated in several solutions with different viscosities using femtosecond transient absorption spectroscopy combined with density functional theory and time-dependent density functional theory calculations. It is demonstrated that the nonradiative process, which competes with radiative decay, involves two main stages, namely the restricted intramolecular rotation and internal conversion processes. The intramolecular rotation depends on viscosity and presents a significant restriction. The restricted rotational rate is determined to be dozens of picoseconds. The following nonradiative process is strongly dominated by intramolecular rotation. The nonradiative decay rate will decrease with the increase in viscosity, leading to a rise in the radiative probability and photoluminous yield. These results have borne out the mechanism of ultrafast restricted intramolecular rotation of aggregation induced emission and provided a detailed photophysical picture of nonradiative processes. [ABSTRACT FROM AUTHOR]

Warm dense matter is a highly energetic phase characterized by strong correlations, thermal effects, and quantum mechanical electrons. Thermal density functional theory is commonly used in simulations of this challenging phase, driving the development of temperature-dependent approximations to the exchange–correlation free energy. Approaches using the adiabatic connection formula are well known at zero temperature and have been recently leveraged at non-zero temperatures as well. In this work, a generalized thermal adiabatic connection (GTAC) formula is proposed, introducing a fictitious temperature parameter. This allows extraction of the exchange–correlation entropy SXC using simulated interaction strength scaling. This procedure uses a Hellmann–Feynman approach to express the exchange–correlation entropy in terms of a temperature- and interaction strength-dependent exchange–correlation potential energy. In addition, analysis of SXC as a function of interaction strength suggests new forms for approximations, and GTAC itself offers a new framework for exploring both the exact and approximate interplay of temperature, density, and interaction strength across a wide range of conditions. [ABSTRACT FROM AUTHOR]

Molecular crystals are difficult to model with accurate first-principles methods due to large unit cells. On the other hand, accurate modeling is required as polymorphs often differ by only 1 kJ/mol. Machine learning interatomic potentials promise to provide accuracy of the baseline first-principles methods with a cost lower by orders of magnitude. Using the existing databases of the density functional theory calculations for molecular crystals and molecules, we train global machine learning interatomic potentials, usable for any molecular crystal. We test the performance of the potentials on experimental benchmarks and show that they perform better than classical force fields and, in some cases, are comparable to the density functional theory calculations. [ABSTRACT FROM AUTHOR]

While computational screening with density functional theory (DFT) is frequently employed for the screening of metal–organic frameworks (MOFs) for gas separation and storage, commonly applied generalized gradient approximations (GGAs) exhibit self-interaction errors, which hinder the predictions of adsorption energies. We investigate the Hubbard U parameter to augment DFT calculations for full periodic MOFs, targeting a more precise modeling of gas molecule–MOF interactions, specifically for N2, CO2, and O2. We introduce a calibration scheme for the U parameter, which is tailored for each MOF, by leveraging higher-level calculations on the secondary building unit (SBU) of the MOF. When applied to the full periodic MOF, the U parameter calibrated against hybrid HSE06 calculations of SBUs successfully reproduces hybrid-quality calculations of the adsorption energy of the periodic MOF. The mean absolute deviation of adsorption energies reduces from 0.13 eV for a standard GGA treatment to 0.06 eV with the calibrated U, demonstrating the utility of the calibration procedure when applied to the full MOF structure. Furthermore, attempting to use coupled cluster singles and doubles with perturbative triples calculations of isolated SBUs for this calibration procedure shows varying degrees of success in predicting the experimental heat of adsorption. It improves accuracy for N2 adsorption for cases of overbinding, whereas its impact on CO2 is minimal, and ambiguities in spin state assignment hinder consistent improvements of O2 adsorption. Our findings emphasize the limitations of cluster models and advocate the use of full periodic MOF systems with a calibrated U parameter, providing a more comprehensive understanding of gas adsorption in MOFs. [ABSTRACT FROM AUTHOR]

Tetrahedrally bonded III-N and related alloys are useful for a wide range of applications from optoelectronics to dielectric electromechanics. Heterostructural AlN-based alloys offer unique properties for piezoelectrics, ferroelectrics, and other emerging applications. Atomic-scale point defects and impurities can strongly affect the functional properties of materials, and therefore, it is crucial to understand the nature of these defects and the mechanisms through which their concentrations may be controlled in AlN-based alloys. In this study, we employ density functional theory with alloy modeling and point defect calculations to investigate native point defects and unintentional impurities in Al 1 − x Gd x N alloys. Among the native defects that introduce deep midgap states, nitrogen vacancies (V N ) are predicted to be in the highest concentration, especially under N-poor growth conditions. We predict and experimentally demonstrate that V N formation can be suppressed in thin films through growth in N-rich environments. We also find that Al 1 − x Gd x N alloys are prone to high levels of unintentional O incorporation, which indirectly leads to even higher concentrations of deep defects. Growth under N-rich/reducing conditions is predicted to minimize and partially alleviate the effects of O incorporation. The results of this study provide valuable insights into the defect behavior in wurtzite nitride-based alloys, which can guide their design and optimization for various applications. [ABSTRACT FROM AUTHOR]

Metal–Organic Polymers (MOPs) have attracted growing attention for lithium-ion battery (LIB) applications due to their merits in orderly ionic transportation and robust structure stability in electrochemical reactions. However, they suffer from poor electronic conductivity. In this work, we apply first-principles density functional theory to explore the potential of three one-dimensional (1D) electrically conductive C6H2S4TM (TM = Fe, Co, and Ni) MOPs with the π–d conjugated coordination as anode materials for Li+ ions storage. Our theoretical results reveal that these 1D MOPs possess a superior theoretical capacity of over 748 mA h g−1. In particular, the 1D C6H2S4Ni MOP shows an exceptional theoretical specific capacity of 1110 mA h g−1 based on the three-electron transferring reaction, which significantly outperforms the traditional graphite-based anode material in LIBs. Moreover, the resonant charge transfer between Ni metal and ligand within the 1D C6H2S4Ni MOP reduces the diffusion energy barrier of the Li atoms when they migrate on the surface of the MOP. The ultrahigh theoretical specific capacity of the C6H2S4Ni MOP predicts that it can be a promising anode material for LIBs. [ABSTRACT FROM AUTHOR]

Rare-earth doped materials are of immense interest for their potential applications in linear and nonlinear photonics. There is also intense interest in sub-nanometer gold clusters due to their enhanced stability and unique optical, magnetic, and catalytic properties. To leverage their emergent properties, here we report a systematic study of the geometries, stability, electronic, magnetic, and linear and nonlinear optical properties of Au5RE (RE = Sc, Y, La–Lu) clusters using density-functional theory. Several low-energy isomers consisting of planar or non-planar configurations are identified. For most doped clusters, the non-planar configuration is energetically favored. In the case of La-, Pm-, Gd-, and Ho-doped clusters, a competition between planar and non-planar isomers is predicted. A distinct preference for the planar configuration is predicted for Au5Eu, Au5Sm, Au5Tb, Au5Tm, and Au5Yb. The distinction between the planar and non-planar configurations is highlighted by the calculated highest frequencies, with the stretching mode of the non-planar configuration predicted to be stiffer than the planar configuration. The bonding analysis reveals the dominance of the RE-d orbitals in the formation of frontier molecular orbitals, which, in turn, facilitates retaining the magnetic characteristics governed by RE-f orbitals, preventing spin-quenching of rare earths in the doped clusters. In addition, the doped clusters exhibit small energy gaps between frontier orbitals, large dipole moments, and enhanced hyperpolarizability compared to the host cluster. [ABSTRACT FROM AUTHOR]

In the interstellar medium, diols and other prebiotic molecules adsorb onto icy mantles surrounding dust grains. Water in the ice may affect the reactivity and photoionization of these diols. Ethylene glycol (EG), 1,2-propylene glycol, and 1,3-propylene glycol clusters with water clusters were used as a proxy to study these interactions. The diol–water clusters were generated in a continuous supersonic molecular beam, photoionized by synchrotron-based vacuum ultraviolet light from the Advanced Light Source, and subsequently detected by reflectron time-of-flight mass spectrometry. The appearance energies for the detected clusters were determined from the mass spectra, collected at increasing photon energy. Clusters of both diol fragments and unfragmented diols with water were detected. The lowest energy geometry optimized conformers for the observed EG–water clusters and EG fragment–water clusters have been visualized using density functional theory (DFT), providing insight into hydrogen bonding networks and how these affect fragmentation and appearance energy. As the number of water molecules clustered around EG fragments (m/z 31 and 32) increased, the appearance energy for the cluster decreased, indicating a stabilization by water. This trend was supported by DFT calculations. Fragment clusters from 1,2-propylene glycol exhibited a similar trend, but with a smaller energy decrease, and no trend was observed from 1,3-propylene glycol. We discuss and suggest that the reactivity and photoionization of diols in the presence of water depend on the size of the diol, the location of the hydroxyl group, and the number of waters clustered around the diol. [ABSTRACT FROM AUTHOR]

A hybrid quantum mechanics/molecular mechanics setup was used to model electronically excited pentacene in the crystal phase. Particularly interesting in the context of singlet fission (SF) is the energetic location of the antiferromagnetically coupled multiexcitonic singlet state, 1(TT), and the ferromagnetically coupled analog in relation to the optically bright singlet state. To provide photophysical properties of the accessible spin manifold, combined density functional theory and multi-reference configuration interaction calculations were performed on pentacene dimers and a trimer, electrostatically embedded in the crystal. The likelihood of a quintet intermediate in the SF process was estimated by computing singlet–quintet electron spin–spin couplings employing the Breit–Pauli Hamiltonian. The performance of the applied methods was assessed on the pentacene monomer. The character of the optically bright state and the energetic location of the 1(TT) state depend strongly on the relative orientation of the pentacene units. In the V-shaped dimers and in the trimer, the optically bright state is dominated by local and charge transfer (CT) excitations, with admixtures of doubly excited configurations. The CT excitations gain weight upon geometry relaxation, thus supporting a CT-mediated SF mechanism as the primary step of the SF process. For the slip-stacked dimer, the energetic order of the bright and the 1(TT) states swaps upon geometry relaxation, indicating strong nonadiabatic coupling close to the Franck–Condon region—a prerequisite for a coherent SF process. The multiexcitonic singlet, triplet, and quintet states are energetically too far apart and their spin–spin couplings are too small to bring about a noteworthy multiplicity mixing. [ABSTRACT FROM AUTHOR]

Tert-butyl functional groups can modulate the self-assembly behavior of organic molecules on surfaces. However, the precise construction of supramolecular architectures through their controlled thermal removal remains a challenge. Herein, we precisely controlled the removal amount of tert-butyl groups in tetraazaperopyrene derivatives by stepwise annealing on Ag(111). The evolution of 4tBu-TAPP supramolecular self-assembly from the grid-like structure composed of 3tBu-TAPP through the honeycomb network formed by 2tBu-TAPP to the one-dimensional chain co-assembled by tBu-TAPP and TAPP was successfully realized. This series of supramolecular nanostructures were directly visualized by high resolution scanning tunneling microscopy. Tip manipulation and density functional theory calculations show that the formation of honeycomb network structure can be attributed to the van der Waals interactions, N–Ag–N coordination bonds, and weak C–H⋯N hydrogen bonds. Further addition of two tert-butyl groups (6tBu-TAPP) leads to a completely different assembly evolution, due to the fact that the additional tert-butyl groups affect the molecular adsorption behavior and ultimately induce desorption. This work can possibly be exploited in constructing stable and long-range ordered nanostructures in surface-assisted systems, which can also promote the development of nanostructures in functional molecular devices. [ABSTRACT FROM AUTHOR]

The direct conversion of methane to methanol has attracted increasing interest due to abundant and low-cost natural gas resources. Herein, by anchoring Cr-oxo/-oxyhydroxides on UiO-66 metal–organic frameworks, we demonstrate that reactive anionic oxyl radicals can be formed by controlling the coordination environment based on the results of density functional theory calculations. The anionic oxyl radicals produced at the completely oxidized CrVI site acted as the active species for facile methane activation. The thermodynamically stable CrVI-oxo/-oxyhydroxides with the anionic oxyl radicals catalyze the activation of the methane C–H bond through a homolytic mechanism. An analysis of the results showed that the catalytic performance of the active oxyl species correlates with the reaction energy of methane activation and H adsorption energies. Following methanol formation, N2O can regenerate the active sites on the most stable CrVI oxyhydroxides, i.e., the Cr(O)4Hf species. The present study demonstrated that the anionic oxyl radicals formed on the anchored CrVI oxyhydroxides by tuning the coordination environment enabled facile methane activation and facilitated methanol production. [ABSTRACT FROM AUTHOR]

QM/MM methods have been used to study electronic structure properties and chemical reactivity in complex molecular systems where direct electronic structure calculations are not feasible. In our previous work, we showed that non-polarizable force fields, by design, describe intermolecular interactions through pairwise interactions, overlooking many-body interactions involving three or more particles. In contrast, polarizable force fields account partially for many-body effects through polarization, but still handle van der Waals and permanent electrostatic interactions pairwise. We showed that despite those limitations, polarizable and non-polarizable force fields can reproduce relative cooperativity achieved using density functional theory due to error compensation mechanisms. In this contribution, we assess the performance of QM/MM methods in reproducing these phenomena. Our study highlights the significance of the QM region size and force field choice in QM/MM calculations, emphasizing the importance of parameter validation to obtain accurate interaction energy predictions. [ABSTRACT FROM AUTHOR]

We present a new library designed to provide a simple and straightforward way to implement QM/AMOEBA (Atomic Multipole Optimized Energetics for Biomolecular Applications) and other polarizable QM/MM (Molecular Mechanics) methods based on induced point dipoles. The library, herein referred to as OpenMMPol, is free and open-sourced and is engineered to address the increasing demand for accurate and efficient QM/MM simulations. OpenMMPol is specifically designed to allow polarizable QM/MM calculations of ground state energies and gradients and excitation properties. Key features of OpenMMPol include a modular architecture facilitating extensibility, parallel computing capabilities for enhanced performance on modern cluster architectures, a user-friendly interface for intuitive implementation, and a simple and flexible structure for providing input data. To show the capabilities offered by the library, we present an interface with PySCF to perform QM/AMOEBA molecular dynamics, geometry optimization, and excited-state calculation based on (time-dependent) density functional theory. [ABSTRACT FROM AUTHOR]

VO2 is renowned for its electric transition from an insulating monoclinic (M1) phase, characterized by V–V dimerized structures, to a metallic rutile (R) phase above 340 K. This transition is accompanied by a magnetic change: the M1 phase exhibits a non-magnetic spin-singlet state, while the R phase exhibits a state with local magnetic moments. Simultaneous simulation of the structural, electric, and magnetic properties of this compound is of fundamental importance, but the M1 phase alone has posed a significant challenge to the density functional theory (DFT). In this study, we show none of the commonly used DFT functionals, including those combined with on-site Hubbard U to treat 3d electrons better, can accurately predict the V–V dimer length. The spin-restricted method tends to overestimate the strength of the V–V bonds, resulting in a small V–V bond length. Conversely, the spin-symmetry-breaking method exhibits the opposite trends. Each of these two bond-calculation methods underscores one of the two contentious mechanisms, i.e., Peierls lattice distortion or Mott localization due to electron–electron repulsion, involved in the metal–insulator transition in VO2. To elucidate the challenges encountered in DFT, we also employ an effective Hamiltonian that integrates one-dimensional magnetic sites, thereby revealing the inherent difficulties linked with the DFT computations. [ABSTRACT FROM AUTHOR]

Finite-temperature calculations are relevant for rationalizing material properties, yet they are computationally expensive because large system sizes or long simulation times are typically required. Circumventing the need for performing many explicit first-principles calculations, tight-binding and machine-learning models for the electronic structure emerged as promising alternatives, but transferability of such methods to elevated temperatures in a data-efficient way remains a great challenge. In this work, we suggest a tight-binding model for efficient and accurate calculations of temperature-dependent properties of semiconductors. Our approach utilizes physics-informed modeling of the electronic structure in the form of hybrid-orbital basis functions and numerically integrating atomic orbitals for the distance dependence of matrix elements. We show that these design choices lead to a tight-binding model with a minimal amount of parameters that are straightforwardly optimized using density functional theory or alternative electronic-structure methods. The temperature transferability of our model is tested by applying it to existing molecular-dynamics trajectories without explicitly fitting temperature-dependent data and comparison with density functional theory. We utilize it together with machine-learning molecular dynamics and hybrid density functional theory for the prototypical semiconductor gallium arsenide. We find that including the effects of thermal expansion on the onsite terms of the tight-binding model is important in order to accurately describe electronic properties at elevated temperatures in comparison with experiment. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys are under consideration for applications where materials are subjected to high temperatures and levels of radiation, such as in the fusion power sector. However, at present, their scope is limited because they are highly brittle at room temperature. One suggested route to mitigate this issue is by alloying with Ti. In this theoretical study, using a computationally efficient linear-response theory based on density functional theory calculations of the electronic structure of the disordered alloys, we study the nature of atomic short-range order in these multi-component materials, as well as assessing their overall phase stability. Our analysis enables direct inference of phase transitions in addition to the extraction of an atomistic, pairwise model of the internal energy of an alloy suitable for study via, e.g., Monte Carlo simulations. Once Ti is added into either the NbMoTaW or VNbMoTaW system, we find that there is competition between chemical phase ordering and segregation. These results shed light on observed chemical inhomogeneity in experimental samples, as well as providing fundamental insight into the physics of these complex systems. [ABSTRACT FROM AUTHOR]

VO2 is renowned for its electric transition from an insulating monoclinic (M1) phase, characterized by V–V dimerized structures, to a metallic rutile (R) phase above 340 K. This transition is accompanied by a magnetic change: the M1 phase exhibits a non-magnetic spin-singlet state, while the R phase exhibits a state with local magnetic moments. Simultaneous simulation of the structural, electric, and magnetic properties of this compound is of fundamental importance, but the M1 phase alone has posed a significant challenge to the density functional theory (DFT). In this study, we show none of the commonly used DFT functionals, including those combined with on-site Hubbard U to treat 3d electrons better, can accurately predict the V–V dimer length. The spin-restricted method tends to overestimate the strength of the V–V bonds, resulting in a small V–V bond length. Conversely, the spin-symmetry-breaking method exhibits the opposite trends. Each of these two bond-calculation methods underscores one of the two contentious mechanisms, i.e., Peierls lattice distortion or Mott localization due to electron–electron repulsion, involved in the metal–insulator transition in VO2. To elucidate the challenges encountered in DFT, we also employ an effective Hamiltonian that integrates one-dimensional magnetic sites, thereby revealing the inherent difficulties linked with the DFT computations. [ABSTRACT FROM AUTHOR]

Polymorph engineering involves the manipulation of material properties through controlled structural modification and is a candidate technique for creating unique two-dimensional transition metal dichalcogenide (TMDC) nanodevices. Despite its promise, polymorph engineering of magnetic TMDC monolayers has not yet been demonstrated. Here we grow FeSe2 monolayers via molecular beam epitaxy and find that they have great promise for magnetic polymorph engineering. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we find that FeSe2 monolayers predominantly display a 1T' structural polymorph at 5 K. Application of voltage pulses from an STM tip causes a local, reversible transition from the 1T' phase to the 1T phase. Density functional theory calculations suggest that this single-layer structural phase transition is accompanied by a magnetic transition from an antiferromagnetic to a ferromagnetic configuration. These results open new possibilities for creating functional magnetic devices with TMDC monolayers via polymorph engineering.

Layered or chain materials have received significant research attention owing to their interesting physical properties, which can dramatically change when the material is thinned from bulk (three-dimensional) to thin two-dimensional sheet or one-dimensional (1D) chain form. Materials with the stoichiometry AX2 with A = Si or Ge and X = S or Se form an especially intriguing semiconducting class. For example, bulk silicon dichalcogenides (SiX2) consist of 1D chains held together by van der Waals forces. Although this structural configuration has the potential to reveal interesting physical phenomena within the 1D limit, obtaining SiX2 single chains has been challenging. We here examine experimentally and theoretically SiX2 materials in the low chain number limit. Carbon nanotubes serve as growth templates and stabilize and protect the structures, and atomic-resolution scanning transmission electron microscopy directly identifies the atomic structure. Two distinct chain structures are observed for SiX2. SixGe1-xS2(1-y)Se2y quaternary alloy chains are also synthesized and characterized, demonstrating tunable semiconducting properties at the atomic-chain level. Density functional theory calculations reveal that the band gap of these alloy chains can be widely tuned through composition engineering. This work offers the possibilities for synthesizing and controlling semiconductor compositions at the single-chain limit to tailor material properties.

A new polymorph of 1,3-diacetylpyrene has been obtained from its melt and thoroughly characterized using single-crystal X-ray diffraction, steady-state UV-Vis spectroscopy and periodic density functional theory calculations. Experimental studies covered the temperature range from 90 to 390 K and the pressure range from atmospheric to 4.08 GPa. Optimal sample placement in a diamond anvil cell according to our previously presented methodology ensured over 80% data coverage up to 0.8 Å for a monoclinic sample. Unrestrained Hirshfeld atom refinement of the high-pressure crystal structures was successful and anharmonic behavior of carbonyl oxygen atoms was observed. Unlike the previously characterized polymorph, the structure of 2°AP-β is based on infinite π-stacks of antiparallel 2°AP molecules. 2°AP-β displays piezochromism and piezofluorochromism which are directly related to the variation in interplanar distances within the π-stacking. The importance of weak intermolecular interactions is reflected in the substantial negative thermal expansion coefficient of -55.8 (57) MK-1 in the direction of C-H...O interactions.

This study focuses on the recognition and isolation of fullerenes, which are crucial for further exploration of their physical and chemical properties. Our goal is to investigate the potential recognition of the D5h–C70 fullerene using crown-shaped metal compositions through density functional theory calculations. We assess the effectiveness of fullerene C70 recognition by studying the binding energy. Additionally, various analyses were conducted, including natural bond order charge analysis and reduced density gradient analysis, to understand the interaction mechanism between the host and guest molecules. These investigations provide valuable insights into the nature of the interaction and the stability of the host–guest system. To facilitate the release of the fullerene guest molecule, the vis–NIR spectra were simulated for the host–guest structures. This analysis offers guidance on the specific wavelengths that can be utilized to release the fullerene guest from the host–guest structures. Overall, this work proposes a new strategy for the effective recognition of various fullerene molecules and their subsequent release from host–guest systems. These findings could potentially be applied in assemblies involving fullerenes, advancing their practical applications. [ABSTRACT FROM AUTHOR]

As typical representatives of group III chalcogenides, InSe, α-In2Se3, and β′-In2Se3 have drawn considerable interest in the domain of photoelectrochemistry. However, the microscopic mechanisms of carrier dynamics in these systems remain largely unexplored. In this work, we first reveal that hot electrons in the three systems have different cooling rate stages and long-lived hot electrons, through the utilization of density functional theory calculations and nonadiabatic molecular dynamics simulations. Furthermore, the ferroelectric polarization of α-In2Se3 weakens the nonadiabatic coupling of the nonradioactive recombination, successfully competing with the narrow bandgap and slow dephasing process, and achieving both high optical absorption efficiency and long carrier lifetime. In addition, we demonstrate that the ferroelectric polarization of α-In2Se3 not only enables the formation of the double type-II band alignment in the InSe/α-In2Se3/InSe heterostructure, with the top and bottom InSe sublayers acting as acceptors and donors, respectively, but also eliminates the hindrance of the built-in electric field at the interface, facilitating an ultrafast interlayer carrier transfer in the heterojunction. This work establishes an atomic mechanism of carrier dynamics in InSe, α-In2Se3, and β′-In2Se3 and the regulatory role of the ferroelectric polarization on the charge carrier dynamics, providing a guideline for the design of photoelectronic materials. [ABSTRACT FROM AUTHOR]

We performed Monte Carlo and dynamic Monte Carlo simulations to model the diffusion of monodispersed suspensions composed of impenetrable cuboidal particles, specifically hard board-like particles (HBPs), in the presence of parallel hard walls. The impact of the walls was investigated by adjusting the size of the simulation box while maintaining constant packing fractions, fixed at η = 0.150, for systems consisting of HBPs with prolate, dual-shaped, and oblate geometries. We observed that increasing the distance between the walls led to the recovery of an isotropic bulk phase, while local particle organization near the walls remained stable. Due to their shape, oblate HBPs exhibit more efficient anchoring at wall surfaces compared to prolate shapes. The formation of nematic-like particle assemblies near the walls, confirmed by theoretical calculations based on density functional theory, significantly influenced local particle dynamics. This effect was particularly pronounced to the extent that a modest portion of cuboids near the walls tended to diffuse exclusively in planes parallel to the confinement, even more efficiently than observed in the bulk regions. [ABSTRACT FROM AUTHOR]

Pt-based alloys, such as Pt3Ni, are among the best electrocatalysts for oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells. Doping of PtNi alloys with Zr was shown to enhance the durability of the operating ORR catalysts. Rationalizing these observations is hindered by the absence of atomic-level data for these tri-metallic materials, even when not exposed to the fuel cell operation conditions. This study aims at understanding structure–property relations in Zr-doped PtNi nanoparticles as a key to their ORR function. In particular, we calculated, using a method based on density functional theory, the most stable chemical orderings of pristine and Zr-doped Pt3Ni particles containing over 400 atoms. We thus clarify (i) preferential location and charge states of Zr atoms in the Pt3Ni NPs; (ii) effect of doping Zr atoms on the stability of the Pt skin of the Pt3Ni NPs; (iii) charge redistribution induced by Zr dopants; (iv) layer-by-layer atomic ordering in the Pt3Ni/Zr NPs with the increasing Zr content; and (v) effect of Zr atoms on the adsorption energies of O and OH species as indicators of the ORR activity. [ABSTRACT FROM AUTHOR]

The increasing presence of 1,1,1,2-tetrafluoroethane (CF3CH2F) in the atmosphere has prompted detailed studies into its complex photodissociation behavior. Experiments focusing on CF3CH2F irradiation have unveiled an array of ions, with the persistent observation of the rearrangement product CHF2+ not yet fully understood. In this work, we combine density functional theory, coupled-cluster calculations with a complete basis set formalism, and atom-centered density matrix propagation molecular dynamics to investigate the energetics and dynamics of different potential pathways leading to CHF2+. We found that the two-body dissociation pathway involving an HF rearrangement, which was previously considered complex for CHF2+ formation, is actually straightforward but not likely due to the facile loss of HF. In contrast, our calculations reveal that the H elimination pathway, once thought of as a potential route to CHF2+, is not only comparably disadvantageous from both thermodynamic and kinetic points of view but also does not align with experimental data, particularly the lack of a rebound peak at m/z 101–102. We establish that the formation of CHF2+ is predominantly via the HF elimination channel, a conclusion experimentally corroborated by studies involving the trifluoroethylene cation CF2CHF+, a key intermediate in this process. [ABSTRACT FROM AUTHOR]

The theory of analytic gradients is presented for the projector-based density functional theory (DFT) embedding approach utilizing the Huzinaga-equation. The advantages of the Huzinaga-equation-based formulation are demonstrated. In particular, it is shown that the projector employed does not appear in the Lagrangian, and the potential risk of numerical problems is avoided at the evaluation of the gradients. The efficient implementation of the analytic gradient theory is presented for approaches where hybrid DFT, second-order Møller–Plesset perturbation theory, or double hybrid DFT are embedded in lower-level DFT environments. To demonstrate the applicability of the method and to gain insight into its accuracy, it is applied to equilibrium geometry optimizations, transition state searches, and potential energy surface scans. Our results show that bond lengths and angles converge rapidly with the size of the embedded system. While providing structural parameters close to high-level quality for the embedded atoms, the embedding approach has the potential to relax the coordinates of the environment as well. Our demonstrations on a 171-atom zeolite and a 570-atom protein system show that the Huzinaga-equation-based embedding can accelerate (double) hybrid gradient computations by an order of magnitude with sufficient active regions and enables affordable force evaluations or geometry optimizations for molecules of hundreds of atoms. [ABSTRACT FROM AUTHOR]

Incorporating self-interaction corrections (SIC) significantly improves chemical reaction barrier height predictions made using density functional theory methods. We present a detailed orbital-by-orbital analysis of these corrections for three semi-local density functional approximations (DFAs) situated on the three lowest rungs of Jacob's ladder of approximations. The analysis is based on Fermi–Löwdin Orbital Self-Interaction Correction (FLOSIC) calculations performed at several steps along the reaction pathway from the reactants (R) to the transition state (TS) to the products (P) for four representative reactions selected from the BH76 benchmark set. For all three functionals, the major contribution to self-interaction corrections of the barrier heights can be traced to stretched bond orbitals that develop near the TS configuration. The magnitude of the ratio of the self-exchange–correlation energy to the self-Hartree energy (XC/H) for a given orbital is introduced as an indicator of one-electron self-interaction error. XC/H = 1.0 implies that an orbital's self-exchange–correlation energy exactly cancels its self-Hartree energy and that the orbital, therefore, makes no contribution to the SIC in the FLOSIC scheme. For the practical DFAs studied here, XC/H spans a range of values. The largest values are obtained for stretched or strongly lobed orbitals. We show that significant differences in XC/H for corresponding orbitals in the R, TS, and P configurations can be used to identify the major contributors to the SIC of barrier heights and reaction energies. Based on such comparisons, we suggest that barrier height predictions made using the strongly constrained and appropriately normed meta-generalized gradient approximation may have attained the best accuracy possible for a semi-local functional using the Perdew–Zunger SIC approach. [ABSTRACT FROM AUTHOR]

To address the challenge of performance portability and facilitate the implementation of electronic structure solvers, we developed the basic matrix library (BML) and Parallel, Rapid O(N), and Graph-based Recursive Electronic Structure Solver (PROGRESS) library. The BML implements linear algebra operations necessary for electronic structure kernels using a unified user interface for various matrix formats (dense and sparse) and architectures (CPUs and GPUs). Focusing on density functional theory and tight-binding models, PROGRESS implements several solvers for computing the single-particle density matrix and relies on BML. In this paper, we describe the general strategies used for these implementations on various computer architectures, using OpenMP target functionalities on GPUs, in conjunction with third-party libraries to handle performance critical numerical kernels. We demonstrate the portability of this approach and its performance in benchmark problems. [ABSTRACT FROM AUTHOR]

This study focuses on the recognition and isolation of fullerenes, which are crucial for further exploration of their physical and chemical properties. Our goal is to investigate the potential recognition of the D5h–C70 fullerene using crown-shaped metal compositions through density functional theory calculations. We assess the effectiveness of fullerene C70 recognition by studying the binding energy. Additionally, various analyses were conducted, including natural bond order charge analysis and reduced density gradient analysis, to understand the interaction mechanism between the host and guest molecules. These investigations provide valuable insights into the nature of the interaction and the stability of the host–guest system. To facilitate the release of the fullerene guest molecule, the vis–NIR spectra were simulated for the host–guest structures. This analysis offers guidance on the specific wavelengths that can be utilized to release the fullerene guest from the host–guest structures. Overall, this work proposes a new strategy for the effective recognition of various fullerene molecules and their subsequent release from host–guest systems. These findings could potentially be applied in assemblies involving fullerenes, advancing their practical applications. [ABSTRACT FROM AUTHOR]

The combined influence of spin–orbit coupling and spatial inversion asymmetry leads to an enhancement of electronic properties, including Rashba spin-splittings as well as spin Hall effect. Recent research has shown the possibility to create two-dimensional Janus materials with inherent structural asymmetry. In this work, the structural stability, piezoelectricity, electronic properties, and intrinsic spin Hall conductivity of quintuple-layer atomic Janus Sb2XSX' (X, X' = S, Se, Te; X ≠ X') monolayers are investigated using first-principles calculations within the framework of density functional theory. They demonstrate relatively high in-plane piezoelectric coefficients ( d 22) and also possess out-of-plane piezoelectric coefficients ( d 31), which is due to the breaking of inversion symmetry in the crystal structure with the space group P3m1. Large Rashba parameters are obtained in Janus Sb2XSX' monolayers, especially high for Sb 2 S 2 Te (1.62 eV Å) and Sb 2 SeSTe (1.33 eV Å) due to strong spin–orbit coupling. Moreover, Rashba-like spin-splitting is also observed in the edge-states as well, which is highest for Sb 2 SeSTe with 2.17 eV Å. Furthermore, Sb 2 S 2 Te and Sb 2 SeSTe monolayers reveal a significantly high Berry curvature (65.59 and 61.05 Bohr 2), spin Berry curvature (− 118.4 and − 120.6 Bohr 2), and spin Hall conductivity (1.8 and 1.6 e 2 /h). Our results suggest that Janus Sb 2 S 2 Te and Sb 2 SeSTe monolayers could be an excellent platform for multifunctional electronic applications. [ABSTRACT FROM AUTHOR]

The electronic structures of three highly mismatched alloys (HMAs)—GeC(Sn), Ga(In)NAs, and BGa(In)As—were studied using density functional theory with HSE06 hybrid functionals, with an emphasis on the local environment near the mismatched, highly electronegative atom (B, C, and N). These alloys are known for their counterintuitive reduction in the bandgap when adding the smaller atom, due to a band anticrossing (BAC) or splitting of the conduction band. Surprisingly, the existence of band splitting was found to be completely unrelated to the local displacement of the lattice ions near the mismatched atom. Furthermore, in BGaAs, the reduction in the bandgap due to BAC was weaker than the increase due to the lattice constant, which has not been observed among other HMAs but may explain differences among experimental reports. While local distortion in GeC and GaNAs was not the cause for BAC, it was found to enhance the bandgap reduction due to BAC. This work also found that mere contrast in electronegativity between neighboring atoms does not induce BAC. In fact, surrounding the electronegative atom with elements of even smaller electronegativity than the host (e.g., Sn or In) consistently decreased or even eliminated BAC. For a fixed composition, moving Sn toward C and In toward either N or B was always energetically favorable and increased the bandgap, consistent with experimental annealing results. Such rearrangement also delocalized the conduction band wavefunctions near the mismatched atom to resemble the original host states in unperturbed Ge or GaAs, causing the BAC to progressively weaken. These collective results were consistent whether the mismatched atom was a cation (N), anion (B), or fully covalent (C), varying only with the magnitude of its electronegativity, with B having the least effect. The effects can be explained by charge screening of the mismatched atom's deep electrostatic potential. Together, these results help explain differences in the bandgap and other properties reported for HMAs from different groups and provide insight into the creation of materials with designer properties. [ABSTRACT FROM AUTHOR]

Fluorescence-encoded infrared (FEIR) spectroscopy is a recently developed technique for solution-phase vibrational spectroscopy with detection sensitivity at the single-molecule level. While its spectroscopic information content and important criteria for its practical experimental optimization have been identified, a general understanding of the electronic and nuclear properties required for highly sensitive detection, i.e., what makes a molecule a "good FEIR chromophore," is lacking. This work explores the molecular factors that determine FEIR vibrational activity and assesses computational approaches for its prediction. We employ density functional theory (DFT) and its time-dependent version (TD-DFT) to compute vibrational and electronic transition dipole moments, their relative orientation, and the Franck–Condon factors involved in FEIR activity. We apply these methods to compute the FEIR activities of normal modes of chromophores from the coumarin family and compare these predictions with experimental FEIR cross sections. We discuss the extent to which we can use computational models to predict the FEIR activity of individual vibrations in a candidate molecule. The results discussed in this work provide the groundwork for computational strategies for choosing FEIR vibrational probes or informing the structure of designer chromophores for single-molecule spectroscopic applications. [ABSTRACT FROM AUTHOR]

Electrocatalytically reducing CO2 into value-added products is a challenging but promising process. Catalysts have been proposed to reduce the potential necessary for the reaction to occur, among which single-atom alloys (SAAs) are particularly promising. Here, we employ density functional theory calculations and the computational electrode model to predict whether silver-based SAAs have the potential to be effective electrocatalysts to convert CO2 into C1 products. We take into account surface defects by using the Ag(211) surface as a model. We also verify whether the proposed materials are prone to OH poisoning or enhance the competing hydrogen evolution reaction. Our calculations predict that these materials show weak mixing between the host and the dopant, characterized by a sharp peak in the density of states near the Fermi energy, except when copper (also a coinage metal) is used as the dopant. This affects the adsorption energy of the different intermediate molecules, yielding different reaction profiles for each substrate. As non-doped silver, copper-doped SAA tends to spontaneously desorb carbon monoxide (CO) instead of proceeding with its reduction. Other elements of the fourth period (Fe, Co, and Ni) tend to bind to the CO molecule but do not favor more reduced products. These metals also tend to enhance the hydrogen evolution reaction. On the contrary, we show that the Ir and Rh dopants have significant potential as electrocatalysts, which favors the reduction of CO over its desorption while also suppressing the hydrogen evolution reaction at potentials lower than those required by copper. They have also been shown to not be prone to poisoning by OH radicals. [ABSTRACT FROM AUTHOR]

Uranium-based materials are valuable assets in the energy, medical, and military industries. However, understanding their sensitivity to hydrogen embrittlement is particularly challenging due to the toxicity of uranium and the computationally expensive nature of quantum-based methods generally required to study such processes. In this regard, we have developed a Chebyshev Interaction Model for Efficient Simulation (ChIMES) that can be employed to compute energies and forces of U and UH3 bulk structures with vacancies and hydrogen interstitials with accuracy similar to that of Density Functional Theory (DFT) while yielding linear scaling and orders of magnitude improvement in computational efficiency. We show that the bulk structural parameters, uranium and hydrogen vacancy formation energies, and diffusion barriers predicted by the ChIMES potential are in strong agreement with the reference DFT data. We then use ChIMES to conduct molecular dynamics simulations of the temperature-dependent diffusion of a hydrogen interstitial and determine the corresponding diffusion activation energy. Our model has particular significance in studies of actinides and other high-Z materials, where there is a strong need for computationally efficient methods to bridge length and time scales between experiments and quantum theory. [ABSTRACT FROM AUTHOR]

ReaxFF reactive force field bridges the gap between nonreactive molecular simulations and quantum mechanical calculations and has been widely applied during the past two decades. However, its application to earth materials, especially those under high T-P conditions relevant to Earth's interior, is still limited due to the lack of available parameters. Here, we present the development and validation of a ReaxFF force field containing several of the most common elements in Earth's crust, i.e., Si/Al/O/H/Na/K. The force field was trained against a large data set obtained from density functional theory (DFT) calculations, including charges, bond/angle distortion curves, equation of states, ion migration energy profiles, and condensation reaction energies. Different coordination environments were considered in the training set. The fitting results showed that the current force field can well reproduce the DFT data (the Pearson correlation coefficient, Rp, is 0.95). We validated the force field on mineral–water interfaces, hydrous melts/supercritical geofluids, and bulk crystals. It was found that the current force field performed excellently in predicting the structural, thermodynamic, and transport properties of various systems (Rp = 0.95). Moreover, possible applications and future development have been discussed. The results obtained in this study suggest that the current force field holds good promise to model a wide range of processes and thus open opportunities to advance the application of ReaxFF in earth material modeling. [ABSTRACT FROM AUTHOR]

We energetically predict the morphology of Pd, Ag, Au, and Pt nanoparticles on (0001) sapphire substrates, using density functional theory (DFT) simulations and the well-known Young–Dupre equation. In all cases, the contact angles exceed 90 ° , indicating that the nanoparticles are spherical. Notably, Au nanoparticles exhibit a higher contact angle than those of their counterparts. The validity of the proposed a b i n i t i o nanoparticle morphology prediction approach based on DFT simulations was assessed in comparison with our previous experimental findings pertaining to the time variation of the full width at half maximum (FWHM) of the resonant peak. Furthermore, the diffusivities of single Pd, Ag, Au, and Pt atoms on the substrate were evaluated by calculating the activation energy, offering insights into the underlying physics governing the timing of FWHM peaks. The analysis confirms a higher diffusivity of Au and Ag compared with Pd and Pt. According to the comparison between DFT and experiment results, although no clear relation is observed between the contact angles and timing of FWHM peaks, the diffusivity of sputtered atoms may influence the timing of FWHM peaks. Thus, timing can help to clarify the nanoparticle size, rather than shape. [ABSTRACT FROM AUTHOR]

Functional thin films of nanoscale metal pillars in oxide or nitride matrices known as vertically aligned nanocomposite (VAN) have gained much interest owing to their unique strain-coupled and highly anisotropic properties. So far, the deposition of these films has been explored mostly experimentally. In this work, a density functional theory (DFT)-based kinetic Monte Carlo simulation model using Bortz–Kalos–Lebowitz algorithm was developed to understand the growth of VAN films deposited by pulsed laser technique on mismatching substrates. The model has been parameterized and applied to understand the kinetics of growth thin films consisting of Au pillars in CeO2 matrix deposited on SrTiO3 substrates. The effects of pulsed laser deposition (PLD) conditions including the pulse frequency, deposition flux, and substrate temperature were explored. The simulations indicate that the Au pillar size and shape exhibit significant dependence on the PLD conditions. Namely, increasing the temperature increases the average pillar size and lowers the pillar density, and vice versa. In addition, the simulations revealed that increasing the deposition rate results in lowering the average pillar size and increasing the density. Particularly, the DFT results suggest that Au pillar size can be tuned during the initial growth of the first monolayer due to the significantly low activation barrier. Our analysis showed that the relationship between the average pillar size and pillar density is influenced by the kinetics. Furthermore, autocorrelation analysis showed that pillars self-organize in quasi-ordered patterns at certain windows of the deposition conditions, which is attributed to the complex nature of the chemical interactions in the system, the kinetics, and the deposition parameters. [ABSTRACT FROM AUTHOR]

Controlling triplet states is crucial to improve the efficiency and lifetime of organic room temperature phosphorescence (ORTP). Although the intrinsic factors from intramolecular radiative and non-radiative decay have been intensively investigated, the extrinsic factors that affect triplet exciton quenching are rarely reported. Diffusion to the defect sites inside the crystal or at the crystal surface may bring about quenching of triplet exciton. Here, the phosphorescence lifetime is found to have a negative correlation with the triplet exciton diffusion coefficient based on the density functional theory (DFT)/time-dependent density functional theory (TD-DFT) calculations on a series of ORTP materials. For systems with a weak charge transfer (CT) characteristic, close π–π stacking will lead to strong triplet coupling and fast triplet exciton diffusion in most cases, which is detrimental to the phosphorescence lifetime. Notably, for intramolcular donor–acceptor (D–A) type systems with a CT characteristic, intermolecular D–A stacking results in ultra-small triplet coupling, thus contributing to slow triplet diffusion and long phosphorescence lifetime. These findings shed some light on molecular design toward high-efficiency long persistent ORTP. [ABSTRACT FROM AUTHOR]

Using density functional theory, we study the preferential ordering of rod-like guest particles immersed in a smectic host fluid. Within a model of perfectly aligned rods and assuming that the guest particles do not perturb the smectic host fluid, simple excluded-volume arguments explain that guest particles that are comparable in length to the host particles order in phase with the smectic host density layering, whereas guest particles that are considerably shorter or longer order in antiphase. The corresponding free-energy minima are separated by energetic barriers on the order of the thermal energy kBT, suggesting that guest particles undergo hopping-type diffusion between adjacent smectic layers. Upon introducing a slight orientational mismatch between the guest particles and the perfectly aligned smectic host, an additional, smaller free-energy barrier emerges for a range of intermediate guest-to-host length ratios, which splits the free-energy minimum into two. Guest particles in this range occupy positions intermediate between in-phase ordering and in-antiphase ordering. Finally, we use Kramers' theory to identify slow, fast, and intermediate diffusive regimes for the guest particles as a function of their length. Our model is in qualitative agreement with experiment and simulation and provides an alternative, complementary explanation in terms of a free-energy landscape for the intermediate diffusive regime, which was previously hypothesized to result from temporary caging effects [M. Chiappini, E. Grelet, and M. Dijkstra, Phys. Rev. Lett. 124, 087801 (2020)]. We argue that our simple model of aligned rods captures the salient features of incommensurate-length guest particles in a smectic host if a slight orientational mismatch is introduced. [ABSTRACT FROM AUTHOR]

We report a detailed density functional theory and molecular dynamics study of hydrogen bonding between trehalose and water, with a special emphasis on interactions in the amorphous solid state. For comparison, water–water interactions in water dimers and tetramers are evaluated using quantum calculations. The results show that the hydrogen bonding energy is dependent not only on the geometry (bond length and angle) but also on the local environment of the hydrogen bond. This is seen in quantum calculations of complexes in vacuum as well as in amorphous solid states with periodic boundary conditions. The temperature-induced glass transition in the trehalose–water system was studied using molecular dynamics simulations with varying cooling and heating rates. The obtained parameters of the glass transition are in good agreement with the experiments. Moreover, the dehydration of trehalose in the glassy state was investigated through a gradual dehydration with multiple small steps under isothermal conditions. From these simulations, the values of water sorption energy at different temperatures were obtained. The partial molar enthalpy of mixing of water value of −18 kJ/mol found in calorimetric experiments was accurately reproduced in these simulations. These findings are discussed in light of the hydrogen bonding data in the system. We conclude that the observed exothermic effect is due to different responses of liquid and glassy matrices to perturbations associated with the addition or removal of water molecules. [ABSTRACT FROM AUTHOR]

Hydration and, in particular, the coordination number of a metal ion is of paramount importance as it defines many of its (bio)physicochemical properties. It is not only essential for understanding its behavior in aqueous solutions but also determines the metal ion reference state and its binding energy to (bio)molecules. In this paper, for divalent metal cations Ca 2 + , Cd 2 + , Cu 2 + , Fe 2 + , Hg 2 + , Mg 2 + , Ni 2 + , Pb 2 + , and Zn 2 + , we compare two approaches for predicting hydration numbers: (1) a mixed explicit/continuum DFT-D3//COSMO-RS solvation model and (2) density functional theory based ab initio molecular dynamics. The former approach is employed to calculate the Gibbs free energy change for the sequential hydration reactions, starting from [M( H 2 O)2]2+ aqua complexes to [M( H 2 O) 9]2+, allowing explicit water molecules to bind in the first or second coordination sphere and determining the most stable [M( H 2 O) n]2+ structure. In the latter approach, the hydration number is obtained by integrating the ion–water radial distribution function. With a couple of exceptions, the metal ion hydration numbers predicted by the two approaches are in mutual agreement, as well as in agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Golden nanoparticle dimers connected by conjugated molecular linkers 1,2-bis(2-pyridyl)ethylene are produced. The formation of stable dimers with 22 nm diameter nanoparticles is confirmed by transmission electron microphotography. The possibility of charge transfer through the linkers between the particles in the dimers is shown by the density functional theory calculations. In addition to localized plasmon resonance of solitary nanoparticles with a wavelength of 530 nm, the optical spectra exhibit a new intense absorption peak in the near-infrared range with a wavelength of ∼780 nm. The emergent absorption peak is attributed to the charge-transfer plasmon (CTP) mode; the spectra simulated within the CTP developed model agree with the experimental ones. This resonant absorption may be of interest to biomedical applications due to its position in the so-called transmission window of biological tissues. The in vitro heating of CTP dimer solution by a laser diode with a wavelength of 792 nm proved the efficiency of CTP dimers for achieving a temperature increase of ΔT = 6 °C, which is sufficient for hyperthermia treatment of malignant tumors. This indicates the possibility of using hyperthermia to treat malignant tumors using the material we synthesized. [ABSTRACT FROM AUTHOR]