Search

An NNP created by the active learning scheme was used to assist the exploration of the conformational space of sodiated pyranoses. As a result, more than 17 000 distinct local minima at the DFT level were located and an NNP with an accuracy of 1 kJ mol−1 was created.

A self-adapting first-principles exploration to understand the mechanism of collision-induced dissociation (CID) in mono-saccharides assisted with neural network potentials (NNP).

We propose a new method that utilizes the database of stable conformers and borrow the fragmentation concept of many-body-expansion (MBE) methods in ab initio methods to train a deep-learning machine learning (ML) model using SchNet.

Collision-induced dissociation of fructose is studied with experiments and first-principles kinetic modeling. The preference for dehydration cannot be easily predicted by the relative orientation of the OH groups as done for aldohexoses.

In this work, we analyze the vibrational spectra of ammonium, methylammonium, and dimethylammonium ions solvated by either water molecules or bisulfate anions using anharmonic vibrational algorithms. Rich and complicated spectral features in the 2700-3200 cm

The aggregates of monofluorinated phenylacetylenes in the gas-phase, investigated using the IR-UV double resonance spectroscopic method in combination with extensive structural search and electronic structure calculations, reveal the formation of liquid-like clusters with a π-stacked dimeric core. The structural assignment based on the IR spectra in the acetylenic and aromatic C–H stretching regions suggests that, unlike the parent non-fluorinated phenylacetylene, the substitution of a F atom on the phenyl ring increases the dipole moment, leading to robustness in the formation of a π⋯π stacked dimer, which propagates incorporating C–H⋯π_{Ar/Ac} and C–H⋯F interactions involving both acetylenic and aromatic C–H groups. The structural evolution of fluorophenylacetylene aggregates in the gas phase shows marginal effects due to fluorine atom position on the phenyl ring, with substitution in the para-position tending towards phenylacetylene. The present study signifies that the π⋯π stacked dimers act as a nucleus for the growth of higher clusters to which other molecular units are added predominantly via the {Ar}_C–H⋯π_{Ar} type of interaction and the dominant interactions present in the crystal structures gradually emerge with increasing cluster size. Based on these features, gas-phase clusters of fluorophenylacetylene are hypothesized as “liquid-like clusters” acting as intermediates in the generation of various polymorphic forms starting from a π⋯π stacked dimer as the core molecular unit.

Studies have debated what is a favorable cluster size in liquid methanol. Applications of the quantum cluster equilibrium (QCE) model on a limited set of cluster structures have demonstrated the dominance of cyclic hexamers in liquid methanol. In this study, we examined the aforementioned question by integrating our implementation of QCE with a molecular-dynamics-based structural searching scheme. QCE simulations were performed using a database comprising extensively searched stable conformers of (MeOH)n for n = 2-14, which were optimized by B3LYP/6-31+G(d,p) with and without the dispersion correction. Our analysis indicated that an octamer structure can contribute significantly to cluster probability. By reoptimizing selected conformers with high probability at the MP2 level, we found that the aforementioned octamer became the dominant species due to favorable vibrational free energy, which was attributed to modes of intermolecular vibration.

The methylammonium ion (CH3NH3+, or noted as MA–H+) is one of the smallest organic ammonium ions that play important roles in organic–inorganic halide perovskites. Despite the simple structure, the vibrational spectra of MA–H+ exhibit complicated features in the 3 μm region which are sensitive to the solvation environment. In the present work, we have applied the ab initio anharmonic algorithm at the CCSD/aug-cc-pVDZ level to simulate the IR and Raman spectra of the solvated methylammonium ion, MA–H+⋯X3, where X denotes the solvent molecules, to understand the Fermi resonance mechanism in which the overtones of NH bending modes are coupled with the fundamentals of NH stretching modes. The spectral features of the solvated clusters with proper solvent species resemble those observed in the perovskite crystal, indicating that they have similar solvation environments and hydrogen bond interactions. Therefore, a linkage between the gas-phase cluster models and the condensed-phase materials can be established, and our simulations and anharmonic analyses help in interpreting the spectral assignments of the observed IR and Raman spectra of perovskites reliably. Furthermore, we have extended this approach to the SFG spectra to demonstrate the selective appearance of bands depending on both the beam polarization configurations and the symmetry of vibrational modes.

In this work, we probed the lithium and sodium intercalation properties in monolayer-stacked NbSe2 bilayer homostructure configurations for their potential application as anode materials in lithium and sodium ion batteries. Similar to known monolayer transition metal dichalcogenides, such as VS2, the structural phase transition barrier of NbSe2 from 1H to 1T is strengthened by lithium and sodium adsorption, implying that it is robust under multiple charging and discharging processes. As multi-layer, stacked 2D materials are more relevant to experiments and their intended applications, four bilayer homostructure stackings were constructed based on the alignment of Nb and Se. All four bilayer homostructure stackings were found to significantly enhance the binding of lithium and sodium at the van der Waals interface, and thus potentially increase the theoretical specific energy capacity of NbSe2via bilayer stacking. In terms of ionic diffusion, it is observed that for all of the bilayer homostructure configurations the diffusion energy barrier for lithium and sodium generally increased compared to the monolayer case. The nature of the stacking appears to affect the diffusion energy barrier with a value of as high as 1.94 eV in the case of sodium for the AB full stacking (compared to 0.08 eV for the monolayer). It is inferred that although the bilayer homostructure stacking of NbSe2 could significantly increase the theoretical specific energy capacity for both lithium and sodium, its drawback is the slowing down of the ion kinetics at the van der Waals interface, which are also important in the charging and discharging processes of a battery system.

In this study, we have examined the adsorption properties of hydrogen on pristine Sc2C monolayers by DFT calculations. Based on these calculations, we have proposed a thermodynamic model to estimate the hydrogen storage capability within the typical ranges for the operating temperature and pressure. Our thermodynamic modeling has shown that the maximum uptake of usable hydrogen could reach up to 7.2 wt% under cryogenic conditions. When calculating the usable hydrogen uptake, we have taken into consideration that, under realistic operating conditions, not all hydrogen adsorbed on pristine Sc2C can be desorbed from the surface, as some surface-adsorbate interactions are too strong. On the other hand, the interaction between the usable hydrogen and Sc2C appears to be too weak to reach the targets for the year 2025 set by the US Department of Energy (5.5 wt% at operating temperatures between 233 K and 358 K and delivery pressures of up to 12 bar). According to the modeling results, one needs to decrease the temperature to 120 K to reach 5.5 wt% hydrogen uptake at 12 bar. The results obtained with the thermodynamic model have been confirmed with a kinetic Monte Carlo simulation, which has also been used to estimate the time scale of the hydrogen adsorption and desorption processes. In addition, we have also evaluated the changes in the electronic structure of the Sc2C monolayer upon adsorbing hydrogen. As the band gap of Sc2C changes significantly upon adsorbing H2, Sc2C may have more potential as a hydrogen detector instead of as a hydrogen storage material.

A series of Zn/Cu Zeolitic Imidazolate Frameworks (ZIFs) ZIF-202, -203, and -204 are systematically investigated by Density Functional Theory (DFT) with and without van der Waals (vdW) corrections. The elastic constants for non-solvent structures indicate that ZIF-202 and -204 are mechanically stable while ZIF-203 is unstable, which arises from the stiffness along the x-axis under a uniaxial strain in the PBE-D3 method. By considering the presence of solvents in ZIF-203, a structural phase transformation from a monoclinic to a triclinic structure is found which could be explained by the Jahn-Teller distortion. From the chemical bonding point of view, it is found that vdW interactions and hybridization between d-orbitals (copper) and p-orbitals (imidazolate) are the main-driving forces in stabilizing ZIF-202 and -204, respectively. The electronic structure calculations predict the presence of two optical transitions in the visible region in agreement with the experimental observation for ZIF-204 both without and with water. The DFT simulations reveal that CO2 molecules prefer to locate near imidazolate and water in dry and hydrated ZIF-204, respectively. The analysis of Canonical Monte Carlo (GCMC) simulations reveals that Coulomb interaction between CO2 and H2O molecules is mainly responsible for the enhanced CO2 uptake and selectivity under humid conditions compared to dry ones.

Strong coupling between stretching fundamentals and bending overtones of vibrational modes, known as Fermi resonance (FR), has been observed for proton motions in the protonated trimethylamine-water cluster. To investigate the role of FR, we examined the vibrational spectra of other three protonated ammonia/amine-water clusters, including the NH4+ ion and its mono- and di-methylated analogues, respectively, with and without argon tagging. In these systems, a simple frequency-scaled harmonic oscillator model will predict only one strong band between 2600 and 3200 cm-1 uniquely due to the hydrogen-bonded NH stretching fundamental for a given conformer. In the experimental vibrational spectra, however, multiple sharp bands were observed. Such a discrepancy often leads to the notions of the coexistence of multiple conformers and/or the appearance of an overtone state as a result of FR. In this work, we applied a discrete variable representation (DVR) implementation of ab initio anharmonic algorithms and demonstrated how one N-H+ stretching fundamental can lead to multiple bands as a result of intrinsic anharmonic couplings. A prominent effect of tuning these FR bands and lighting up dark overtone states in this wide frequency range was investigated by changing the number of methyl groups in the protonated amine moiety. The effect of Ar-tagging was also analyzed and decent agreement between the experimental and simulated spectra certified the above-mentioned simple pictures. We also found that the coupling constant for trimethylamine is the largest among these protonated amine-water clusters, and the overall coupling strength decreases as the hydrogen-bonded NH stretching frequency redshifts in the order of dimethylamine, methylamine, and ammonia.

The spectral features of H3O+ between 3000 and 3800 cm-1 are known to be dominated by coupling between the fundamentals of stretching modes and the overtones of bending modes. A strong Fermi resonance (FR) pattern has been observed in Ar-tagged H3O+, and the sensitive dependence of the FR pattern on the number of Ar tags has been analyzed by Li et al. [J. Phys. Chem. A, 2015, 119(44), 10887]. Based on ab initio anharmonic calculations with MP2/aug-cc-pvDZ, Tan et al. investigated the influence of different types of rare gas and found a counter-intuitive trend that the strength of the coupling between the overtones of bending modes and the fundamentals of stretching modes decreases as the strength of solvation increases [Phys. Chem. Chem. Phys., 2016, 18(44), 30721]. In the present work, we combine both experimental and theoretical tools to gain a better understanding of the FR in H3O+. Experimentally, spectra of H3O+ with light and much more weakly-bound Ne tags were measured for the first time and spectra of Ar-tagged H3O+ were re-measured for comparison. Theoretically, we have implemented several computational schemes to improve both the accuracy and efficiency of the anharmonic treatments with higher-level ab initio methods (up to CCSD/aug-cc-pVTZ). With the good agreement between the experimental and theoretical spectra, we are confident about the prediction of the modulation of coupling strength by the solvation environments.

Collision-induced dissociation of sodiated α-glucose, β-glucose, α-galactose, β-galactose, α-mannose, and β-mannose was studied using electronic structure calculations and resonance excitation in a low-pressure linear ion trap. We made an extensive search of conformers and transition states in calculations to ensure the transition state with the lowest barrier height for each dissociation channel could be located. The major dissociation channels, in addition to desodiation, are cross-ring dissociation and dehydration. Cross-ring dissociation starts with H atom transfer from the O1 atom to the O0 atom, followed by the cleavage of the C1-O0 bond. Dehydration of the anomer with O1 and O2 atoms in the cis configuration involves the transfer of an H atom from the O2 atom to the O1 atom, followed by the cleavage of the C1-O1 bond. In contrast, dehydration of the anomer with O1 and O2 atoms in the trans configuration mainly occurs through H atom transfer from the O3 or O2 atom to the O1 atom for glucose, from the O3 or O4 atom to the O1 atom for galactose, and from the O4 or O2 atom to the O1 atom for mannose, followed by the cleavage of the C1-O1 bond. The dehydration barrier heights are lower than those of cross-ring dissociation for cis anomers, but higher than those of cross-ring dissociation for trans anomers. The relative barrier heights from calculations are consistent with the experimental measurements of branching ratios. Both computational and experimental results show that the branching ratio of dehydration can be generalized as a simple rule for rapidly identifying the anomeric configurations of these monosaccharides.

The dissociation of water molecules absorbed on a cleaved non-polar GaN(11[combining macron]00) surface was studied primarily with synchrotron-based photoemission spectra and density-functional-theory calculations. The adsorbed water molecules are spontaneously dissociated into hydrogen atoms and hydroxyl groups at either 300 or 130 K, which implies a negligible activation energy (

The proton-bound nitrogen dimer, N2–H+–N2, and its isotopologues were investigated by means of vibrational spectroscopy. These species were produced upon electron bombardment of mixtures of N2 (or 15N2) and para-hydrogen (p-H2) or normal-D2 (n-D2) during deposition at 3.2 K. Reduced-dimension anharmonic vibrational Schrodinger equations were constructed to account for the strong anharmonic effects in these protonated species. The fundamental lines of proton motions in N2–H+–N2 were observed at 715.0 (NH+N antisymmetric stretch, ν4), 1129.6 (NH+N bend, ν6), and 2352.7 (antisymmetric NN/NN stretch, ν3) cm−1, in agreement with values of 763, 1144, and 2423 cm−1 predicted with anharmonic calculations using the discrete-variable representation (DVR) method at the CCSD/aug-cc-pVDZ level. The lines at 1030.2 and 1395.5 cm−1 were assigned to combination bands involving nν2 + ν4 (n = 1 and 2) according to theoretical calculations; ν2 is the N2⋯N2 stretching mode. For 15N2–H+–15N2 in solid p-H2, the corresponding major lines were observed at 710.0 (ν4), 1016.7 (ν2 + ν4), 1124.3 (ν6), 1384.8 (2ν2 + ν4), and 2274.9 (ν3) cm−1. For N2–D+–N2 in solid n-D2, the corresponding major lines were observed at 494.0 (ν4), 840.7 (ν2 + ν4), 825.5 (ν6), and 2356.2 (ν3) cm−1. In addition, two lines at 762.0 (weak) and 808.3 cm−1 were tentatively assigned to be some modes of N2–H+–N2 perturbed or activated by a third N2 near the proton.

The potential energy surface (PES), structures and thermal properties of methanol clusters (MeOH)n with n = 8–15 were explored by replica-exchange molecular dynamics (REMD) simulations with an empirical model and refined using density functional theory (DFT) methods. For a given size, local minima structures were sampled from REMD trajectories and archived by a newly developed molecular database via a two-stage clustering algorithm (TSCA). Our TSCA utilizes both the topology of O–H⋯O hydrogen bonding networks and the similarity of the shapes to filter out duplicates. The screened molecular database contains only distinct conformers sampled from REMD and their structures are further optimized by the two DFT methods with and without dispersion correction to examine the influence of dispersion on their structures and binding energies. Inspecting different O–H⋯O networks, the binding energies of methanol clusters are highly degenerated. The degeneracy is more significant with the dispersion effect that introduces weaker but more complex C–H⋯O bonds. Based on the structures we have searched, we were able to extract general trends and these datasets can serve as a starting point for further high-level ab initio calculations to reveal the true energy landscape of methanol clusters.

Due to the easy intralayer gliding and weak interlayer van der Waals interaction in transition metal dichalcogenides (TMDs), ion (particularly Li+) intercalation has been used to modify and tune their atomic structures to obtain the desired optical, electronic and chemical properties for future optoelectronics and energy storage applications. A good understanding of the transformative structures during intercalation is critical. In this paper, we investigate the structural transformation dynamics of 2H-MoS2 using electrochemical Li+ intercalation for 2H-MoS2. The introduction of Li+ changes the local symmetry of the MoS2 in favor of the dT phase, clearly indicated by the appearance of Raman peaks of the dT phase. Further Li+ insertion causes the samples to become single-layer-like, characterized by the disappearance of the 32 cm−1 Raman peak. We also observe for the first time that the photoluminescence (PL) emission gradually redshifts with decreasing intensity, followed by eventual vanishing of the PL peak in the dT-MoS2 phase. By the nudged elastic band (NEB) calculations, we propose the 2H–1T–dT phase transition mechanism of MoS2 for Li+ intercalated samples. Our claims are supported by high resolution-transmission electron microscopy (HR-TEM). Our study deepens the understanding of the phase transition dynamics upon lithium intercalation, which is of great value to possible optoelectronic devices based on the phase engineering of TMDs. The new Li-stabilized dT-MoS2 phase does not possess inversion symmetry and may present a feasible way to achieve Weyl state tuning in a single material via phase engineering.

The intermode coupling between shared proton (O-H(+)-O) fundamental stretching and flanking modes in (CH3OH)2H(+) was revisited in the following contexts: (1) evaluation of Hamiltonian matrix elements represented in a "pure state" (PS) basis and (2) tuning of coupling strengths using H/D isotopic substitution. We considered four experimentally accessible isotopologues for this study. These are: (CH3OH)2H(+), (CD3OH)2H(+), (CH3OD)2D(+), and (CD3OD)2D(+). Potential energy surfaces (PESs), as well as dipole moment surfaces (DMSs), were constructed at the MP2/aug-cc-pVDZ level. Multidimensional vibrational calculations were conducted by solving a reduced dimensional Schrödinger equation using a discrete variable representation (DVR). We found that vibrational states in (CH3OH)2H(+) and (CD3OH)2H(+) are much more heavily mixed than those in (CH3OD)2D(+) and (CD3OD)2D(+). Furthermore, each isotopologue chooses to strongly couple between out-of-phase in-plane CH3 rocking and its out-of-plane counterpart. Lastly, the interaction between O-O stretching and O-H(+)-O stretching was explored. We found that between the first overtone of O-O stretching and its combination tone with O-H(+)-O fundamental stretching, only the second couples with O-H(+)-O fundamental stretching. We hope that our isotopologue calculations would motivate experimentalists to measure them in the future.

Liquid methanol and methanol clusters have been comprehensively studied to reveal their local structure and hydrogen bond networks. However, our understanding of the crystal forms of methanol is rather limited. The known crystal structures of solid methanol, α, β, and γ, are composed of infinite hydrogen bond chains in their unit cell. The structural diversity of solid methanol is much less than that of liquid methanol, in which both chain and ring structures exist and have been confirmed by experiments. In this study, we employed ab initio random structure searching (AIRSS) to study possible solid methanol structures. AIRSS predicted known solid methanol phases as well as various ring structures that have not been considered. A new possible candidate structure for the δ phase was also discovered. The relative stability of known solid methanol phases and our newly discovered structures were also investigated through dispersion corrected density functional theory. The density functional calculation provides reliable phase transition pressures between the known phases and the searched structures compared with experimental suggestions. In addition, the simulation result indicated that CH⋯O hydrogen bonds play a major role in stabilizing the methanol crystals under high pressures.

This study demonstrates how the intermode coupling in the hydronium ion (H3O+) is modulated by the composition of the first solvation shell. A series of rare gas solvated hydronium ions (H3O+Rg3, where Rg = Ne, Ar, Kr, and Xe) is examined via reduced-dimensional anharmonic vibrational (RDAV) ab initio calculations. We considered six key vibrational normal modes, namely: a hindered rotation, two H–O–H bends, and three O–H stretches. Between the O–H stretches and the H–O–H bends, the first is more sensitive to solvation strength. Our calculations revealed that the Fermi resonance between the first overtones of O–H bends and the fundamentals of O–H stretches led to complex spectral features from 3000 to 3500 cm−1. Such an interaction is not only sensitive to the type of rare gas messengers surrounding the H3O+ ion, it also exhibits an anomalous H → D isotope effect. Although it is accepted that visible combination tones (∼1900 cm−1) arise from the complex coupling between the hindered rotation and the H–O–H bends, the origin of their intensities is not yet clearly understood. We found that the intensity of these combination tones could be much stronger than their fundamental H–O–H bends. Within our theoretical framework, we tracked the combination tone's intensity back to the asymmetric O–H stretches. This simple notion of intensity borrowing is confirmed by examining eight complexes (H3O+·Rg3 and D3O+·Rg3) with spectral features awaiting experimental confirmations.

Fermi resonance between the N–H stretching (ν1 and ν3) and the overtone of N–H bending (2ν4) in ammonia has hindered the interpretation and assignments of experimental spectra of small ammonia clusters. In this work, we carried out anharmonic vibrational calculations using MP2/aug-cc-pVDZ to examine the vibrational spectra of (NH3)n=1–5 with a focus on the size evolution. The enhancement of hydrogen bond strength due to cooperative effects will cause ν1 and ν4 to red-shift and blue-shift, respectively, when the size of the cluster increases. Our calculations show that the energy order of fundamental of ν1 and overtone of ν4 is reversed between n = 3 and n = 4. Therefore, while the resultant mixed levels do not show remarkable shifts in their peak positions, the main identity of these mixed levels changes and this causes significant re-distribution of their intensities. Furthermore, our ab initio anharmonic calculation scheme can directly evaluate the coupling strength between different N–H stretching and overtone of N–H bending without any experimental parameters, thus leading us to a simpler picture to understand the Fermi resonance in (NH3)n.

We investigated the application of 1T′-MX2 (M = Mo, W; X = S, Se, Te) 2D materials as hydrogen evolution reaction (HER) catalysts using density functional theory. Our results show that 1T′-MX2 have lower energies and are dynamically more stable than their 1T counterparts, therefore likely more relevant to previous experimental findings and applications. We found that sulfides are better catalysts, followed by selenides and tellurides. Specifically, 1T′-MoS2 and WS2 are the best HER catalysts among MX2. We proposed a mechanism, rather than the metallicity surmised previously, based on the calculated density of states. On the other hand, the effectively stretched (compressed) X site on the 1T′ 2 × 1 reconstruction from 1T is shown to be more (less) active for the HER. We further exploited the application of external strain to tune and boost the HER performance. Our findings are of significance in the elucidation of previous experimental studies and exploration of potential materials for clean energy applications.

We investigated the defected two-dimensional materials MoX2 (X = O, S, Se) for hydrogen evolution reaction by first principles calculations. While the basal plane is inert for pristine MoX2, we found that the defected MoX2 can adsorb hydrogen atoms at defect sites, with appropriate adsorption energies for hydrogen evolution. By analyzing density of states and charge density, we showed that a dangling bond state slightly below the Fermi energy emerges when a defect is created. We proposed that this state is responsible for hybridizing with the hydrogen atom 1s state and hence the adsorption. Knowing the mechanism, we further considered tuning the reaction using adatoms (several first-row transition metals, B, C, N, O). We found that C and O adatoms can make defected MoX2 ideal for hydrogen evolution at higher defect levels (H coverage).

In this work, we identified a large number of structurally distinct isomers of midsized deprotonated water clusters, OH(-)(H2O)n=4-7, using first-principles methods. The temperature dependence of the structural variation in the solvation shell of OH(-) for these clusters was examined under the harmonic superposition approximation. We simulated the vibrational and photoelectron spectra based on these thermodynamic calculations. We found that the isomers with 3-coordinated hydroxide dominate the population in these midsized clusters. Furthermore, an increase in temperature causes a topological change from compact isomers with many intermolecular hydrogen bonds to open isomers with fewer but more directional intermolecular hydrogen bonds. We showed that this evolution in structure can be observed through the change in the vibrational spectra at 3200-3400 cm(-1). In addition, the increase in directional hydrogen bonded isomers, which have outer hydration shell with OH bonds pointing to the hydroxide, causes the vertical detachment energy to increase at higher temperatures. Lastly, we also performed studies to understand the variation in the aforementioned spectral quantities with the variation in the coordination number of the hydroxide.

We theoretically explored new two-dimensional materials near the ionic instability (three-dimensional structures are favored), with covalent bonded systems (graphene) sitting at the opposite end of the spectrum. Accordingly, monolayer alkaline earth and transition metal halides, many of their bulk forms being layered structures, were investigated by density functional calculations. We thus predicted a new class of two-dimensional materials by performing structure relaxation, cohesive/formation energy and full phonon dispersion calculations. These materials exhibit strong ionic bonding character, as revealed by significant charge transfers. The superior charge donating/accepting abilities and the large specific area make these new materials promising for adsorption and catalytic reactions. We demonstrated adsorption and diffusion of Li on these materials, which are relevant for Li ion battery electrodes and hydrogen storage. Also the new materials with varied charge donating abilities and their nanostructures can enhance and tune catalytic reactions, such as Ziegler-Natta catalysts. Moreover, they exhibit diverse electronic properties that can be of great application interest, ranging from insulators to metals, and even spin-polarized semiconductors.

The nature of water networks exposed to ionizing radiation is important in various radiation-related chemistry and biology. To understand structural evolution of ionized water networks at the molecular level, we report here infrared spectra of watercluster radical cations (H2O)n+ (n = 3 − 11) in the gas phase. Spectral features of free OH stretch modes are quite similar to those of protonated waterclustersH+(H2O)n, of which the hydrogen-bond network structures have been revealed. In addition, we observed an extra band attributed to the stretch of an OH radical in (H2O)n+. These results indicate that nominal (H2O)n+ should be regarded as H+(H2O)n−1(OH) motifs having similar network shapes to those of H+(H2O)n. We also analyzed hydrogen-bonded OH stretch bands and found that hydrogen-bond strength is a key factor to determine the position of the OH radical relative to the protonated site (H3O+/H5O2+). Because an OH radical is a weaker hydrogen bond acceptor than water, the first solvation shell of the protonated site is preferentially filled with water. As a result, the OH radical is separated from the protonated (charged) site by at least one water molecule in n ≥ 5 clusters. This result shows the instability of the H3O+-OH ion-radical contact pair in water networks, and implies the higher mobility of the OH radical due to its release from the charged site. Observed structural preferences are confirmed both in cold and warm clusterion sources.

Relativistic density functional theory calculations have been conducted to examine the effect of atomic under-coordination on the crystal structure, binding energy, and electron configuration of cuboctahedral and Marks decahedral gold clusters. Trend consistency between calculations and experimental observations confirmed the predictions made using BOLS correlation theory, suggesting that the shorter-and-stronger bonds between under-coordinated atoms induce local structure relaxation, potential well depression, and the associated local charge and energy densification, as well as the polarization of the otherwise conducting s-electrons (valence charge) by the densely- and tightly-trapped core electrons of which the binding energy shifts positively to deeper energies. Findings are in good agreement with scanning tunneling microscopy/spectroscopy results from monomers, dimers, chain ends, and nanostructures of gold and other metals.

By the incorporation of C atoms into (BN)(12) fullerene, our theoretical investigation shows that carbon doped boron nitride cages (BNC) can achieve a high hydrogen storage amount of 7.43 wt%, and dehydrogenation of the corresponding BNC hydrides (BNC(H)) is thermodynamically favored for practical applications of hydrogen energy, making BNC competitive candidates for hydrogen storage materials.

With first-principle DFT calculations, the catalytic activity of heteroatom-doped carbon nanostructures in oxygen reduction reaction is investigated by exploring the active site of B-doped, N-doped and (B, N)-codoped and analyzing the kinetic pathways of oxygen reduction with the participation of protons. It is found that the heteroatom-doped graphene can become the effective catalysis materials for ORR with four-electron pathway. Especially, the formation of epoxide groups may be important for the four-electron processes on B-doped and (B, N)-codoped graphene. By the analysis of charge redistribution, the formation of active catalytic sites is attributed to the localized positive charge and electronic dipole induced by the dopant.

Water decomposition process was investigated by ab initio molecular dynamic simulations using a model of (H(2)O)(2)(+) clusters. The proton transfer (PT) process from the cationic H-donor water to the H-acceptor water for the formation of (HO˙)·H(3)O(+) was predicted as about 90 fs on average calculated at CCSD level of theory. The valence-electron transfer (VET) process through the formation of hemibond interaction between neutral and cationic water, (H(2)O)(2)(+), was also identified in several collected trajectories. Both PT and VET processes were found to propagate along two orthogonal reaction coordinates, the former was through an intermolecular hydrogen bond and the latter required oxygen-oxygen hemibonding. Significant difference of the theoretical electronic transitions along the VET trajectories was also observed in comparison with the non-VET cases, being calculated at SAC-CI level. The strong absorption features of hemibonding (H(2)O)(2)(+) may introduce an interesting consideration for experimental design to monitor the water decomposition process.

To assess the accuracy of density functional theory (DFT) methods in describing hydrogen bonding in condensed phases, we benchmarked their performance in describing phase transitions among different phases of ice. We performed DFT calculations of ice for phases Ih, II, III, VI and VII using BLYP, PW91, PBE, PBE-D, PBEsol, B3LYP, PBE0, and PBE0-D, and compared the calculated phase transition pressures between Ih-II, Ih-III, II-VI, and VI-VII with the 0 K experimental values of Whalley [J. Chem. Phys., 1984, 81, 4087]. From the geometry optimization of many different candidates, we found that the most stable proton orientation as well as the phase transition pressure does not show much functional dependence for the generalized gradient approximation and hybrid functionals. Although all these methods overestimated the phase transition pressure, the addition of van der Waals (vdW) correction using PBE-D and PBE0-D reduced the transition pressure and improved the agreement for Ih-II. On the other hand, energy ordering between VI and VII reversed and gave an unphysical negative transition pressure. Binding energy profiles of a few conformations of water dimers were calculated to understand the improvement for certain transitions and failures for others with the vdW correction. We conclude that vdW dispersion forces must be considered to accurately describe the hydrogen bond in many different phases of ice, but the simple addition of the R(-6) term with a small basis set tends to over stabilize certain geometries giving unphysical ordering in the high density phases.

An edge-modified tight-binding (TB) approximation has been developed, enabling us to clarify the energetic origin of the width-dependent band gap (E(G)) expansion of the armchaired and the reconstructed zigzag-edged graphene nanoribbons with and without hydrogen termination. Consistency between the TB and the density-function theory calculations affirmed that: (i) the E(G) expansion originates from the Hamiltonian perturbation due to the shorter and stronger bonds between undercoordinated atoms, (ii) the combination of the edge-to-width ratio with a local bond strain up to 30% and the associated 152% potential well depression determines the width dependent E(G) change; and, (iii) hydrogen termination affects insignificantly the band gap width as the H-passivation minimizes the midgap impurity states.

The flexible installations of a sulfamate ester on a glycal scaffold at C3, C4, or C6 approaching alpha- or beta-aminoglycosides is communicated. A variety of glycal acceptors (O, S, and N) were applied, enhancing the utility of this method as an operationally simple protocol for the stereoselective synthesis of polyfunctionalized alpha- or beta- aminosaccharides.

The low-temperature proton-ordered counterparts for ice-Ih, ice-III, ice-VI and ice-VII are investigated by first principle methods in conjunction with a graph enumeration technique. Two experimentally well calibrated disorder/order transitions, ice-Ih/ice-XI and ice-VII/ice-VIII, are used to validate the methodology we used herein and in both cases our approach is able to reproduce major experimental features. For ice-III and ice-VI, direct structural determination on the fully proton-ordered counterparts by neutron diffraction is not available and in the literature different ordering schemes have been proposed. Our calculation results serve as an independent reference, and we shall discuss our findings and their relevance to previous experimental works.