Hao Ren（任浩）

Structural stability is one of the most fundamental issues to explore the applications of two-dimensional (2D) materials. Se-terminated bismuth oxychalcogenide, Bi2O2Se, attracts extensive attention as its quasi-2D nature, which links traditional three-dimensional (3D) and van de Waals 2D materials. Herein, we systematically constructed Bi2O2Se monolayers with different surface Se concentrations and studied their structural stability under different chemical environments. The stability of Bi2O2Se monolayer is found to be sensitive to the surface Se concentration, i.e., its formation energy decreases linearly until the Se concentration increases to 50% and then remains flat. Five monolayers with 0%, 12.5%, 50%, 87.5% and 100% Se concentrations are found to be highly stable at different chemical environments from Se-poor to Se-rich. Among them, the 50% Se concentration is high-symmetry with a neat Bisingle …

Terahertz (THz) absorption is a fingerprint property of materials, due to the underlying low-frequency vibration/phonon modes being strongly dependent on the chemical constitutions and microscopic structures. The low excitation energies (0.414−41.4 meV) are related to two intrinsic properties of THz vibrations: the potential energy surfaces (PESs) are shallow, and the vibrationally excited states are usually populated via thermal fluctuations. The shallow PESs make the vibrations usually anharmonic, leading to redshifted vibrational excited state absorption; combined with considerable vibrational excited states population, characteristic THz signals are usually redshifted and congested with varying degrees at different temperatures. Combining existing experimental THz spectra at low temperatures, first principles vibration analysis, and the Morse potential, we developed a semi-empirical model to evaluate the …

Base pair mismatch has been regarded as the main source of DNA point mutations, where minor short-lived tautomers were usually involved. However, the detection and characterization of these unnatural species pose challenges to existing techniques. Here, by using systematic structural and ultrafast resonance Raman (RR) spectral analysis for the four possible conformers of guanine-cytosine base pairs, the prominent marker Raman bands were identified. We found that the hydrogen bonding vibrational region from 2300 cm−1 to 3700 cm−1 is ideal for the identification of these short live species. The marker bands provide direct evidence for the existence of the tautomer species, thus offering an effective strategy to detect the short-lived minor species. Ultrafast resonance Raman spectroscopy would be a powerful tool to provide direct evidence of critical dynamical details of complex systems involving protonation …

The terahertz (THz) region vibration spectral signatures of molecular crystals can usually be ascribed to the low-frequency vibrational modes related to weak intermolecular interactions, e.g. van der Waals (vdW) interactions or hydrogen bonding. These interactions collectively dictate the compositional units deviating from their equilibrium configurations. The collective movements are intrinsically long-range, and hence the boundary conditions used for theoretical calculation can affect the corresponding potential energy gradients and alter the vibrational features. In this work, we constructed a series of finite-sized cluster models with varying sizes and an extended periodic crystal model for L-ascorbic acid (L-AA) crystals. Density functionals with both semi-local contributions and nonlocal vdW terms, implemented with either atom-centered Gaussian basis or plane waves, were tested. By comparing first principles …

The performance of lithium-sulfur battery is restricted by the lower value of electrode conductance and the sluggish LiPSs degradation kinetics. Unfortunately, the degradation rate of polysulfides was mostly attributed to the catalytic energy barrier in previous, which is unable to give accurate predictions on the performance of lithium-sulfur battery. Thereby, a quantitative framework relating the battery performance to catalytic energy barrier and electrical conductivity of the cathode host is developed here to quantitate the tendency. As the model compound, calculated-Ti4O7 (c-Ti4O7) has the highest comprehensive index with excellent electrical conductivity, although the catalytic energy barrier is not ideal. Through inputting the experimental properties such as impedance and charge/discharge data into the as-build model, the final conclusion is still in line with our prediction that Ti4O7 host shows the most excellent …

Photocatalytic reduction of CO2 to renewable energy is considered as one of the important strategies to simultaneously solve the problems of environmental pollution and energy shortage. However, high carrier recombination probability and low product selectivity seriously affect the further development of this technique. Here, we propose a novel 2D In2S2X (X = Se, Te) Janus structure catalyst. It exhibits excellent photocatalytic performance: (a) The valence band maximum and the conduction band minimum are contributed by the bottom and top atoms, respectively, so the photogenerated electrons have a bottom-up transition direction. The intrinsic polarization makes In2S2X have a built-in electric field opposite to the electron transition direction, so it extremely promotes the separation of carriers and inhibits electrons-holes recombination. (b) More importantly, the vacancy concentration on the catalyst surface can …

Chemical bonding properties are crucial to understanding the chemical behavior of molecules. Spectroscopy is a versatile technical tool to study various microscopic properties, but its interpretation suffers from human biases and the loss of high-dimensional information. Here, we present a machine learning approach to predict diverse bonding properties, including the bond dissociation energy, bond length, and α-C connectivity of hydroxyls in organic molecules, by fusing multiple spectra with different physical mechanisms. Combining nuclear magnetic resonance and vibrational spectroscopy exhibits higher prediction accuracy than what they did separately. On the hold-out test data set, the models achieve a mean absolute error of 1.243 kcal/mol and 1.041 × 10–4 Å for BDE and bond length and an accuracy of 95.09% for hydroxyl α-C connectivity. Our models demonstrate strong extrapolation capabilities when …

Harvesting solar energy to convert CO2 into chemicals via photocatalysis has received increasing attention, however, lack of precisely controlled and uniformly dispersed active sites usually leads to low selectivity and activity. Herein, we present an in situ covalent-bonding strategy for the first time to knit well-defined single-site Ru-N2 into conjugated covalent triazine frameworks (CTFs) for highly selective photoreduction of CO2. The resulting Ru-CTF enhanced charge separation and stabilized the molecular catalyst, providing a solar-to-formate conversion rate of 2090 μmol·gcat−1·h−1 with a selectivity of 98.5 % without extra photosensitizer, which greatly outperforms most other reported photocatalysts. Experiments and DFT calculations demonstrate that the single-site Ru-N2 could easily activate CO2 and the H2O-substituted Ru-N2 unit is the newly discovered active center for the efficient photocatalysis. This work …