Prediction of superconductivity in metallic boron-carbon compounds from 0 to 100 GPa by high-throughput screening.

Boron-carbon compounds have been shown to have feasible superconductivity. In our earlier paper [Zheng et al., Phys. Rev. B, 2023, 107, 014508], we identified a new conventional superconductor of LiB3C at 100 GPa. Here, we aim to extend the investigation of possible superconductivity in this structural framework by replacing Li atoms with 27 different cations from periods 3, 4, and 5 under pressures ranging from 0 to 100 GPa. Using the high-throughput screening method of zone-center electron-phonon interaction, we found that ternary compounds like CaB3C, SrB3C, TiB3C, and VB3C are promising candidates for superconductivity. The consecutive calculations using the full Brillouin zone confirm that they have a Tc of <31 K at moderate pressures. Our study demonstrates that fast screening of superconductivity by calculating zone-center electron-phonon coupling strength is an effective strategy for high-throughput identification of new superconductors.

High-Throughput Screening of Strong Electron-Phonon Couplings in Ternary Metal Diborides.

We perform a high-throughput screening on phonon-mediated superconductivity in a ternary metal diboride structure with alkali, alkaline earth, and transition metals. We find 17 ground states and 78 low-energy metastable phases. From fast calculations of zone-center electron-phonon coupling, 43 compounds are revealed to show electron-phonon coupling strength higher than that of MgB2. An anticorrelation between the energetic stability and electron-phonon coupling strength is identified. We suggest two phases, i.e., Li3ZrB8 and Ca3YB8, to be synthesized, which show reasonable energetic stability and superconducting critical temperature.

Quantum spin Hall effect in tilted penta silicene and its isoelectronic substitutions.

Silicene, a competitive two-dimensional (2D) material for future electronic devices, has attracted intensive attention in condensed matter physics. Utilizing an adaptive genetic algorithm (AGA), we identify a topological allotrope of silicene, named tilted penta (tPenta) silicene. Based on first-principles calculations, the geometric and electronic properties of tPenta silicene and its isoelectronic substitutions (Ge, Sn) are investigated. Our results indicate that tPenta silicene exhibits a semimetallic state with distorted Dirac cones in the absence of spin-orbit coupling (SOC). When SOC is considered, it shows semiconducting behavior with a gap opening of 2.4 meV at the Dirac point. Based on the results of invariant ( = 1) and the helical edge states, we demonstrate that tPenta silicene is a topological insulator. Furthermore, the effect of isoelectronic substitutions on tPenta silicene is studied. Two stoichiometric phases, i.e., tPenta Si0.333Ge0.667 and tPenta Si0.333Sn0.667 are found to retain the geometric framework of tPenta silicene and exhibit high stabilities. Our calculations show that both tPenta Si0.333Ge0.667 and tPenta Si0.333Sn0.667 are QSH insulators with enlarged band gaps of 32.5 meV and 94.3 meV, respectively, at the HSE06 level, offering great potential for practical applications at room temperature.

Ground and excited states of even-numbered Hubbard ring at half-filling: comparison of the extended Gutzwiller approach with exact diagonalization.

It remains a great challenge in condensed matter physics to develop a method to treat strongly correlated many-body systems with balanced accuracy and efficiency. We introduce an extended Gutzwiller (EG) method incorporating a manifold technique, which builds an effective manifold of the many-body Hilbert space, to describe the ground-state (GS) and excited-state (ES) properties of strongly correlated electrons. We systematically apply an EG projector onto the GS and ES of a non-interacting system. Diagonalization of the true Hamiltonian within the manifold formed by the resulting EG wavefunctions gives the approximate GS and ES of the correlated system. To validate this technique, we implement it on even-numbered fermionic Hubbard rings at half-filling with periodic boundary conditions, and compare the results with the exact diagonalization (ED) method. The EG method is capable of generating high-quality GS and low-lying ES wavefunctions, as evidenced by the high overlaps of wavefunctions between the EG and ED methods. Favorable comparisons are also achieved for other quantities including the total energy, the double occupancy, the total spin and the staggered magnetization. With the capability of accessing the ESs, the EG method can capture the essential features of the one-electron removal spectral function that contains contributions from states deep in the excited spectrum. Finally, we provide an outlook on the application of this method on large extended systems.

The Gutzwiller conjugate gradient minimization method for correlated electron systems.

We review our recent work on the Gutzwiller conjugate gradient minimization method, anab initioapproach developed for correlated electron systems. The complete formalism has been outlined that allows for a systematic understanding of the method, followed by a discussion of benchmark studies of dimers, one- and two-dimensional single-band Hubbard models. In the end, we present some preliminary results of multi-band Hubbard models and large-basis calculations of F2to illustrate our efforts to further reduce the computational complexity.

A rotationally invariant approach based on Gutzwiller wave function for correlated electron systems.

We introduce a rotationally invariant approach combined with the Gutzwiller conjugate gradient minimization method to study correlated electron systems. In the approach, the Gutzwiller projector is parametrized based on the number of electrons occupying the onsite orbitals instead of the onsite configurations. The approach efficiently groups the onsite orbitals according to their symmetry and greatly reduces the computational complexity, which yields a speedup of20∼50×in the minimal basis energy calculation of dimers. The computationally efficient approach promotes more accurate calculations beyond the minimal basis that is inapplicable in the original approach. A large-basis energy calculation of F2demonstrates favorable agreements with standard quantum-chemical calculations Bytautaset al(2007J. Chem. Phys.127164317).

[Hierarchical first aid training scheme for elementary and middle school students: the practices from the construction of "Baoan Model" social emergency medicine training].

OBJECTIVE: To share the implementation experience of hierarchical first aid training scheme for elementary and middle school students in Baoan District of Shenzhen City and evaluate its effect of training. METHODS: During August 2018 and August 2019, elementary and middle schools students who participated in the first aid training held by emergency rescue training center of Baoan District were enrolled. Baseline information including the number of students, the number of attending tutors, the number of cardiopulmonary resuscitation (CPR) training models, automated external defibrillator (AED) models were recorded. According to hierarchical levels of three age, students received different courses with content from simple to hard: the course of elementary school students was consisting of dialing 120, smart animation on how to identify accidental damage, demonstration of AED and Hemlick techniques, CPR practise (40 minutes). The course of junior high school students was consisted of how to dial 120, how to identify accidental damage and simple disposal, application of CPR and AED, practice CPR and AED and Hemlick techniques (90 minutes). The course of high school students was consisted of how to dial 120, identify accidental damage and right disposal, identification of out-of-hospital cardiac arrest, the key-point of CPR and AED, practice CPR and AED, Hemlick techniques and hemostatic bandage (120 minutes). At the end of course, elementary school students were voluntary for skill assessment; junior high school students only were compulsory for skill assessment in small classes but not required in large classes, just for demonstration; additionally, the whole high school students were compulsory for skill assessment. The characteristics of first aid training students at different levels were collected in order to compare the differences on the usage of CPR training model and AED training model, the distribution of emergency resource, the ratio for passing examination. RESULTS: A total of 12 896 students and 2 086 training instructors took parted in 200 lists of first aid training courses, 8 557 CPR models and 8 493 AED models were used. On average, there are 65.27±5.61 students in each session, and 10.52±10.43 training instructors. There are 43.09±19.06 CPR training models and 42.77±18.61 AED training models. The mean ratio of student to tutor was 6.07±1.47, student to CPR model was 1.54±1.02, and student to AED model was 1.54±1.03. In the end of course, 10 494 students participated in the examination with the participation rate of 81.37%; 10 114 students passed the examination with the passing rate of 96.38%. Hierarchical analysis showed: compare to elementary school students, the average number of junior high school students in every training session significantly increased (cases: 69.94±8.77 vs. 58.69±6.12, P < 0.05), but the average number of high school students in every training session significantly decreased (cases: 57.35±5.79 vs. 58.69±6.12, P < 0.05). The proportion of instructors in junior high school students' training significantly reduced (5.94±1.39 vs. 6.48±2.02, P < 0.05). The examination ratio of junior high school students and high school students was increased significantly [81.07% (6 667/8 224), 100% (2 313/2 313) vs. 64.18% (1 514/2 359), both P < 0.05], but the ratio of passing the examination was significantly reduced [95.47% (6 365/6 667), 96.88% (2 241/2 313) vs. 99.60%(1 508/1 514), both P < 0.01]. This might be related to the low difficulty of elementary school students' assessment and the low proportion of compulsory examination. CONCLUSIONS: Hierarchical scheme is feasible for first aid training in elementary and middle school students, the content of course should be desighed from easy to hard. Synchronously, sufficient training instructors and training models should be equipped to ensure the quality.

Quantum Spin Hall States in Stanene/Ge(111).

For topological insulators to be implemented in practical applications, it is a prerequisite to select suitable substrates that are required to leave insulators' nontrivial properties and sizable opened band gaps (due to spin-orbital couplings) unaltered. Using ab initio calculations, we predict that Ge(111) surface qualified as a candidate to support stanene sheets, because the band structure of √3 × âˆš3 stanene/Ge(111) (2 × 2) surface displays a typical Dirac cone at Γ point in the vicinity of the Fermi level. Aided with the result of Z2 invariant calculations, a √3 × âˆš3 stanene/Ge(111) (2 × 2) system has been proved to sustain the nontrivial topological phase, with the prove being confirmed by the edge state calculations of stanene ribbons. This finding can serve as guidance for epitaxial growth of stanene on substrate and render stanene feasible for practical use as a topological insulator.