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High lattice thermal conductivity of intrinsic GeTe limits the wide application of GeTe-based thermoelectrics. Recently, the optimization of GeTe-based thermoelectric materials has been focusing on reducing lattice thermal conductivity via strengthening phonon scattering. In this study, we systematically studied thermoelectric properties of Se-alloyed Ge0.95Bi0.05Te via theoretical calculations, structural characterizations, and performance evaluations. Our results indicate that Se-alloying can induce dense point defects with mass/strain-field fluctuations and correspondingly enhance point defect phonon scattering of the Ge0.95Bi0.05Te matrix. Se-alloying might also change chemical bonding strength to introduce resonant states in the base frequency of Ge0.95Bi0.05Te matrix, which can strengthen Umklapp phonon scattering. Finally, a decreased lattice thermal conductivity from ∼1.02 W m−1 K−1 to ∼0.65 W m−1 K−1 at 723 K is obtained in Ge0.95Bi0.05Te1-xSex pellets with increasing the Se content from 0 to 0.3. A peak figure of merit of ∼1.6 at 723 K is achieved in Ge0.95Bi0.05Te0.7Se0.3 pellet, which is ∼77% higher than that of pristine GeTe. This study extends the understanding on the thermoelectric performance of GeTe.

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.

A two-dimensional Logistic cosine cascade map (2D-LCCM) and a three-dimensional Logistic cosine cascade map (3D-LCCM) are proposed based on a logistic map and infinite collapse cascade model. We analyze the chaotic properties of 2D-LCCM and 3D-LCCM, such as Lyapunov exponential spectrum, attractors, and complexity, which show that the 2D-LCCM and 3D-LCCM are hyperchaotic and have large chaotic regions. We also proposed a DNA encryption algorithm based on double chaotic maps. 2D-LCCM was used for scrambling and 3D-LCCM for diffusion. First, the sequence no-duplicate zigzag transform (SNZT) is used to scramble the plaintext. Z-transform is applied to the permutation sequence to make the sequence more random. Then a repetition-free permutation associated with the plaintext is applied to each block, and the pixel position is effectively scrambled. Finally, DNA diffusion is performed using DNA coding to diffuse pixel values. Simulation results show that the algorithm has a good encryption effect, high efficiency and anti-interference performance. Therefore, the proposed new hyperchaotic map and DNA encryption algorithm can be effectively applied to the process of image encryption.

The demand for disorder-tolerant quantum logic and spin electronics can be met by generating and controlling dissipationless spin currents protected by topology. Dirac fermions with helical spin-locking surface transport offer a way of achieving such a goal. Yet, surface-bulk coupling can lead to strong Dirac electron scattering with bulk carriers and phonons as well as impurities, assisted by such dissipative channel, which results in “topological breakdown”. Here, we demonstrate that coherent lattice vibrations periodically driven by a single-cycle terahertz (THz) pulse can significantly suppress such dissipative channel in topological insulators. This is achieved by reducing the phase space in the bulk available for Dirac fermion scattering into during coherent lattice oscillations in Bi2Se3. This light-induced suppression manifests as a remarkable transition exclusively in surface transport, absent for bulk, above the THz electric fields for driving coherent phonons, which prolongs the surface transport lifetime. These results, together with simulations, identify the critical role of spin–orbit coupling for the “phase space contraction” mechanism that suppresses the surface-bulk coupling. Imposing vibrational quantum coherence into topological states of matter may become a universal light control principle for reinforcing the symmetry-protected helical transport.

Interactions between defects in graphene and the lattice distortion and electronic charge localization induced by the defect interactions are studied by tight-binding (TB) calculations using the recently developed three-center TB potential model. The interaction between two 5–7 Stone–Wales defects gliding along the zig-zag (ZZ) direction of graphene, which has been observed by experiment, is studied at first to validate the TB calculations. Reconstructed divacancy defect pairs and di-adatom defect pairs separated along the glide ZZ and armchair (AC) directions in graphene, respectively, are then studied. We show that the characteristics (i.e., attractive or repulsive) and the strength of interactions between these defects are dependent on the type of defects and on the direction and distance of the defect separation on graphene. Although elastic interaction due to graphene lattice distortion induced by the defect has significant contribution to the total interaction energy, redistribution of electron char...

The adsorption and wetting on quartz surfaces by aqueous solutions of xylyl-substituted biquaternary ammonium salt gemini surfactants with different spacer groups (C3 and C6), have been investigated. The interfacial properties of surfactant solutions such as contact angle, adhesional tension (γLV cos θ), quartz–water interfacial tension (γSL) as well as adhesion work (WA) have been estimated. The obtained results show that C3 and C6 have similar adsorption behavior on quartz surfaces. Before critical micelle concentration (cmc) is reached, the contact angles of gemini surfactants slowly increase with the increasing concentration, and the adsorption amount at the water–air interface is almost the same as those at a quartz–water interface. After reaching cmc, the gemini surfactant Cn molecules form a more compact adsorption film through bending the flexible spacer chain, instead of forming a bi-layer. As a result, a further increase in quartz–liquid interfacial tension (γSL) and a consequent increase in contact angle have been observed after cmc. Gemini C6 shows a stronger ability towards hydrophobic modification at a quartz surface than C3, demonstrating the contribution of the longer methylene spacer to the hydrophobic modification of the quartz surface.

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 of 20 ∼ 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 F2 demonstrates favorable agreements with standard quantum-chemical calculations Bytautas et al (2007 J. Chem. Phys. 127 164317)

The effect of electronic Coulomb interaction on the phase formation of fcc Ce lattice is investigated by full ab initio calculations without adjustable Coulomb $U$ and $J$ parameters using the Gutzwiller wavefunction-based correlation matrix renormalization theory (CMRT). Its total energy and pressure as a function of volume agree reasonably well with existing $\text{DFT}+\text{Gutzwiller}$ calculations and experiments, indicating correct capture of electronic correlation and screening effects within the CMRT formalism. A stable phase is found in line with the experimental $\ensuremath{\alpha}$-Ce phase, and a lurking phase is identified supposedly linked with the experimental $\ensuremath{\gamma}$-Ce phase. A criterion based on the local $4f$ electron charge fluctuation is introduced to confirm the distinct electronic correlation natures of both phases.

Zr–Rh metallic glass has enabled its many applications in vehicle parts, sports equipment and so on due to its outstanding performance in mechanical property, but the knowledge of the microstructure determining the superb mechanical property remains yet insufficient. Here, we develop a deep neural network potential of Zr–Rh system by using machine learning, which breaks the dilemma between the accuracy and efficiency in molecular dynamics simulations, and greatly improves the simulation scale in both space and time. The results show that the structural features obtained from the neural network method are in good agreement with the cases in ab initio molecular dynamics simulations. Furthermore, we build a large model of 5400 atoms to explore the influences of simulated size and cooling rate on the melt-quenching process of Zr77Rh23. Our study lays a foundation for exploring the complex structures in amorphous Zr77Rh23, which is of great significance for the design and practical application.

Electron-phonon interactions are fundamentally important physical processes responsible for many key discoveries in condensed matter physics and material sciences. Herein, by exploiting the scattering-type scanning near-field optical microscope (s-SNOM) excited with a femtosecond infrared (IR) laser, we explored the strong coupling between IR phonons in few-layer graphene (FLG) with ultrahot electrons, which are heated up by the intense laser field enhanced by the s-SNOM tip. More specifically, we found that the intensity of the phonon resonance can be tuned systematically by varying the laser power that controls the electron temperature. Furthermore, the high spatial resolution of s-SNOM allows us to map the local phonon characteristics at sharp boundaries and nanostructures. Our findings offer insights into the intriguing physics behind the electron-phonon interactions in nonequilibrium conditions and open a pathway for manipulating phonons with optical means.

Van der Waals (vdW) heterostructures, which are produced by the precise assemblies of varieties of two-dimensional (2D) materials, have demonstrated many novel properties and functionalities. Here we report a nano-plasmonic study of vdW heterostructures that were produced by depositing ordered molecular layers of pentacene on top of graphene. We find through nano-infrared (IR) imaging that surface plasmons formed due to the collective oscillations of Dirac fermions in graphene are highly sensitive to the adjacent pentacene layers. In particular, the plasmon wavelength declines systematically but nonlinearly with increasing pentacene thickness. Further analysis and density functional theory (DFT) calculations indicate that the observed peculiar thickness dependence is mainly due to the tunneling-type electron transfer from pentacene to graphene. Our work unveils a new method for tailoring graphene plasmons and deepens our understanding of the intriguing nano-optical phenomena due to interlayer couplings in novel vdW heterostructures., Comment: 21 pages

Phase change memory is an emerging nonvolatile memory technology, recently becoming the center of attention to bridge the speed gap between fast dynamic random access memory and slow flash-based solid-state drives. Lately, CrGeTe3 has been investigated as a special phase change material with an inverse resistance and density change. This material has excellent properties such as good thermal stability, ultralow-energy glass formation process and almost zero mass-density change upon crystallization. Here, we analyzed the amorphous structure of this abnormal material in detail through ab initio simulations and discovered that the metallic-like tight atomic packing is the origin of the high carrier concentration and high mass density in the amorphous phase. Furthermore, the bonding analysis confirms that it is the short Cr–Cr bonds that lead to high packing efficiency in the amorphous local order. Our results discovered the material gene of the amorphous CrGeTe3, paving the way for the design of high-performance memory devices based on this material.

A numerical multiscale model is used to resolve the high computation complexity in the ac loss calculation of large-scale superconducting devices and proves advantageous with regard to time and memory requirements. In the multiscale model, the background field estimation method is of crucial importance to the calculation accuracy. In this paper, we propose four new background field estimation methods, including the Jacobi Gauss- Seidel hybrid and iteration methods, to improve the accuracy and expand the application scope of the multiscale model. A high temperature superconducting solenoid magnet is used to test the performance of these four methods and the results are compared with those of the H-formulation reference model and the multiscale model with a Jo uniform background field estimation method. Results show that in the 19 A/50 Hz ac transport current test case: the Jacobi Gauss- hybrid and iteration methods reduce the error of the ac loss mean value/peak value to 7.88%/5.89%, 5.71%/2.4%, 3.22%/1.22%, and 1.83%/0.69% with the total time cost reduced by 15.7, 8.9, 13.5, and 7.8 times. The multiscale model is expected to achieve even higher accuracy in applications where the ac loss is relatively small due to its coincidence property. The greatly improved accuracy makes the multiscale model a reliable substitute for the H-formulation model. In addition, the idea of iteration and back substitution in background field correction widely expands the application scope of the multiscale model. Alternative background field estimation methods allow the multiscale model to be applied flexibly according to the requirement of the calculation speed and accuracy. The feature of small degrees of freedom resolves the high computation complexity of the ac loss calculation model and reduces the memory requirement. All these merits make the multiscale model competitive in the calculation of ac loss.

The adsorption of xylyl-substituted biquaternary ammonium salt Gemini surfactants with different spacer (C3 and C6) at polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA) surfaces has been investigated and the different adsorption parameters such as surface tension, contact angle, adhesional tension, solid-water interfacial tension and work of adhesion have been estimated. The results show that C3 and C6 have similar adsorption behaviors at PTFE and PMMA surfaces. C3 and C6 adsorb gradually at a PFTE-water interface via hydrophobic interactions and the adsorption amounts at the water-air interface are almost three times higher than those at the PTFE-water interface due to the steric hindrance effect. However, the contact angle keeps constant throughout the experimental concentration range because the decrease in surface tension just counterbalances the decrease in PFTE-water interfacial tension. On the other hand, C3 and C6 adsorb at the PMMA surface via polar interactions between xylyl and functional groups of PMMA before CMC. Similar to PTFE, the increase in PMMA-water interfacial tension compensates the decrease in surface tension and the contact angle also shows a stationary value before the CMC. A bi-layer structure of C3 and C6 will be formed at the PMMA-water interface via hydrophobic interaction and PMMA-water interfacial tension decreases consequently after the CMC, which results in the decrease in contact angle.

The crystal structures of boron hydrides in a pressure range of 50-400 GPa were studied using the genetic algorithm (GA) method combined with first-principles density functional theory calculations. BH4 and BH5 are predicted to be thermodynamically unstable. Two new BH2 structures with Cmcm and C2/c space group symmetries, respectively, were predicted, in which the B atoms tend to form two-dimensional sheets. The calculated band structures showed that in the pressure range of 50-150 GPa, the Cmcm-BH2 phase has very small gaps, while the C2/c-BH2 phase at 200-400 GPa is metallic. The superconductivity of the C2/c-BH2 structure was also investigated, and electron-phonon coupling calculations revealed that the estimated Tc values of C2/c-BH2 are about 28.18-37.31 K at 250 GPa.

Phase-change material such as Ge 2 Sb 2 Te 5 is usually utilized to store data due to the pronounced contrast in optical and electrical properties between crystalline and amorphous phases. As the density differs in the two phases, it is necessary to explore the influence of pressure on the structures of Ge 2 Sb 2 Te 5 , especially for the supercooled liquid which is an inevitable state in the formation of the two phases. The short-range structures in supercooled liquid Ge 2 Sb 2 Te 5 under compression have been investigated by using ab initio molecular dynamics simulation. The supercooled liquid eventually changes to a solid with an increase in pressure. During the process, tetrahedrons decrease slightly, revealing that tetrahedral structures are insensitive to the pressure. Octahedrons increase as the pressure is less than 3.7 GPa and then decrease, suggesting that a moderate pressure can promote the formation of octahedrons. The body-centered-cubic, face-centered-cubic and hexagonal closed-packed structures are observed at 9.9 GPa and then increase gradually. Additionally, it is noticed that Sb- and Te-centered clusters prefer Ge-centered clusters to forming the high-coordinated short-range structures during the compression process. Our research make us aware of the effects of pressure on short-range structures in supercooled liquid, which is of great importance in the application of phase-change materials.

We review our recent work on the Gutzwiller conjugate gradient minimization method, an ab initio approach 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 F2 to illustrate our efforts to further reduce the computational complexity.

Tailored design/fabrication of electroanalytical materials with highly-active exposed crystal planes is of great importance for the development of electrochemical sensing. In this work, combining experimental and theoretical efforts, we reported a facile strategy to fabricate TiO2 nanocrystals with tunable electrochemical performance for heavy metal detection. Density functional theory (DFT) calculations indicated that TiO2 (001) facet showed relative larger adsorption energy and lower diffusion energy barrier toward heavy metal ions, which is favorable for obtaining better electrochemical stripping behaviors. Based on this prediction, a series of TiO2 nanocrystals with different ratios of exposed (001) and (101) facets were synthesized. Electrochemical stripping experiments further demonstrated that with the increase of the percentage of exposed (001) facet, the sensitivity toward Pb(II) and Cd(II) was increased accordingly. When the percentage of exposed (001) facet was increased from 7% to 80%, the sensitivity increased by 190% and 93% for Pb(II) and Cd(II), respectively. Our work provides an effective route to construct advanced electroanalytical materials for sensing.

We studied the electronic structure of ${\mathrm{PtPb}}_{4}$ using laser angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations. This material is closely related to ${\mathrm{PtSn}}_{4}$, which exhibits exotic topological properties such as Dirac node arcs. The Fermi surface (FS) of ${\mathrm{PtPb}}_{4}$ consists of two electron pockets at the center of the Brillouin zone (BZ) and several hole pockets around the zone boundaries. Our ARPES data reveal significant Rashba splitting at the $\mathrm{\ensuremath{\Gamma}}$ point, in agreement with DFT calculations. The presence of Rashba splitting may render this material of potential interest for spintronic applications.

Using carbon-based materials as substrates or additives is an effective strategy for the improvement of electrochemical properties of polypyrrole (PPy) in supercapacitors, while the interfacial interactions between them is not exactly clear, which limits the rational design of composite electrodes. Herein, the interfacial interactions are investigated by forming novel freestanding composite electrodes via depositing PPy on the surface of carbon foam (CF). After combination, the capacitance increases from 37.3 mF cm−2 to 364.0 mF cm−2. Moreover, a superior capacitance retention (99.6%) can be achieved, after 10,000 charging/discharging cycles. Density functional theory (DFT) results show that the introduction of different oxygen-containing functional groups will lead to the difference of adsorption energy between carbon materials and PPy, thus affecting the cycling stability of composite materials. Moreover, the intermolecular interaction also affects redox properties of composite electrodes by changing the composition and energy of frontier orbits of the interfacial complexes involved in redox reactions. This study will provide a new perspective for purposeful regulating the electrochemical performance of composite electrodes.

An appropriate treatment of electronic correlation effects plays an important role in accurate descriptions of physical and chemical properties of real materials. The recently proposed Correlation Matrix Renormalization theory with Sum Rule correction (CMR) for studying correlated electron materails has shown good performance in molecular systems and a periodic Hydrogen chain in comparison with various quantum chemistry and quantum Monte Carlo calculations. This work gives a detailed formulation and computational code implementation of CMR in multi-band periodic lattice systems. This lattice CMR ab initio theory is highly efficient, has no material specific adjustable parameters, and has no double counting issues faced by the hybrid approaches like LDA+U, DFT+DMFT and DFT+GA type theories. Benchmark studies on materials with s and p orbitals in this study show that CMR in its current implementation consistently performs well for these systems as the electron correlation increases from the bonding region to the bond breaking region.

The development of long-range ferromagnetic (FM) order in dilute magnetic topological insulators can induce dissipationless electronic surface transport via the quantum anomalous Hall effect. We measure the magnetic excitations in a prototypical magnetic topological crystalline insulator, ${\mathrm{Sn}}_{0.95}{\mathrm{Mn}}_{0.05}\mathrm{Te}$, using inelastic neutron scattering. Neutron diffraction and magnetization data indicate that our ${\mathrm{Sn}}_{0.95}{\mathrm{Mn}}_{0.05}\mathrm{Te}$ sample has no FM long-range order above a temperature of 2 K. However, we observe slow, collective FM fluctuations $(l70\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{eV})$, indicating proximity to FM order. We also find a series of sharp peaks originating from local excitations of antiferromagnetically (AF) coupled and isolated Mn-Mn dimers with ${J}_{\mathrm{AF}}=460\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{eV}$. The simultaneous presence of collective and localized components in the magnetic spectra highlight different roles for substituted Mn ions, with competition between FM order and the formation of AF-coupled Mn-Mn dimers.

We recently proposed the Gutzwiller conjugate gradient minimisation (GCGM) method for efficient and accurate calculation of the ground state total energy of molecular and bulk systems. The GCGM met...

A 150 kJ/100 kW conduction-cooled HTS superconducting magnetic energy storage magnet, which consists of 17 double pancake coils and operates at 20 K, was developed and manufactured in the Huazhong University of Science and Technology. To evaluate the thermal characteristic of the magnet, this paper conducts a series of experiments and carries out the loss analyses. When the maintaining time and peak value of the flat top current in the magnet are constant, the maximum temperature rise will first decrease and then increase with the continuous augment of the current ramp rate, and it means that there is a valley value for the maximum temperature rise during an operational cycle time including charging, standby, and discharging stages. Similarly, the total losses, which include the ac heat loss and the resistive loss caused by the joints between every two double pancakes and extra resistance of the high temperature superconducting (HTS) coils, will fall with the increase of the ramp rate to its valley value, and then it will increase with the ramp rate. Experimental results show that the temperature variation of the magnet is in keeping with the heat loss variation.

A numerical multiscale model is used for the calculation of ac loss in a two-dimensional (2-D) planar model and proves advantageous with regard to time and memory requirements. In this study, we improve the calculation accuracy and apply a multiscale model to a 2-D axisymmetric model of a high-temperature superconducting solenoid magnet by using an iteration method for the background field estimation. The calculation results are compared with those of the H-formulation model, homogenization model, and multiscale model with a J 0 uniform background field estimation method. The iteration method speeds up the calculation by 7.7 to 12.9 times and reduces the error of the average ac loss to 6.71% and the error of the ac loss peak value to 5.95%. In addition, the iteration method is superior to the homogenization model in terms of calculation speed and accuracy as the computational complexity increases.

Interaction between two hydrogen adatoms on graphene was studied by first-principles calculations. We showed that there is an attraction between two H adatoms on graphene. However, the strength of interaction between two hydrogen adatoms and magnetic properties of graphene are strongly dependent on the residence of the two adatoms on the graphene sublattices. Hydrogen adatoms introduce lattice distortion and electron localization in graphene which mediate the attractive interaction between the two H adatoms.

The Al–Sm system is selected as a model system to study the transition process from liquid and amorphous to crystalline states. In recent work, we have shown that, in addition to long-range translational periodicity, crystal structures display well-defined short-range local atomic packing motifs that transcends liquid, amorphous and crystalline states. In this paper, we investigate the longer range spatial packing of these short-range motifs by studying the interconnections of Sm–Sm networks in different amorphous and crystalline samples obtained from molecular dynamics simulations. In our analysis, we concentrate on Sm–Sm distances in the range ~5.0–7.2 A, corresponding to Sm atoms in the second and third shells of Sm-centred clusters. We discover a number of empirical rules characterising the evolution of Sm networks from the liquid and amorphous states to associated metastable crystalline phases experimentally observed in the initial stages of devitrification of different amorphous samples. As ...

Heusler compounds and alloys based on them are of great recent interest because they exhibit a wide variety of spin structures, magnetic properties, and electron-transport phenomena. Their properties are tunable by alloying and we have investigated L21-orderd compound Ru2MnSn and its alloys by varying the atomic Mn:Sn composition. While antiferromagnetic ordering with a Neel temperature of 361 K was observed in Ru2MnSn, the Mn-poor Ru2Mn0.8Sn1.2 alloy exhibits properties of a diluted antiferromagnet in which there are localized regions of uncompensated Mn spins. Furthermore, a noncoplanar spin structure, evident from a topological Hall-effect contribution to the room-temperature Hall resistivity, is realized in Ru2Mn0.8Sn1.2. Our combined experimental and theoretical analysis shows that in the Ru2Mn0.8Sn1.2 alloy, the magnetic properties can be explained in terms of a noncoplanar antiferromagnetic scissor mode, which creates a small net magnetization in a magnetic field and subsequently yields a Berry curvature with a strong topological Hall effect.

The electronic properties of metal-doped cubic BaTiO3 have been investigated using first-principles calculations. Through systematic analysis on effects of various metals doping through substituting Ti with the main group, 3d and 4d transitions metal atoms, we show that most transition metal doping can effectively reduce the band gap of BaTiO3. The partial density of states analysis indicates that different doping elements have different effects on the band-gap engineering. The effective mass of BaTiO3 before and after doping was further analyzed. And we found that the hole effective mass apparently decrease after Fe, Cu, Zn, Mo, and Ag doping, which could lead to increase of hole mobility and charge transfer enhancement. The calculation results showed that substituting Ti with Fe or Mo would be more effective for improving the photoelectric property of BaTiO3. Our theoretical calculations provide useful insights and beneficial guidance into experimental study of BaTiO3 in the photoelectric applications.

The structures and electronic properties of partial C, Si and Ge decorated graphene were investigated by first-principles calculations. The calculations show that the interaction between graphene and the decoration patches is weak and the semiconductor patches act as agents for weak electron doping without much disturbing graphene electronic π-bands. Redistribution of electrons due to the partial decoration causes the electrostatic potential lower in the decorated graphene areas, thus induced an electric field across the boundary between the decorated and non-decorated domains. Such an alternating electric field can change normal stochastic adatom diffusion to biased diffusion, leading to selective mass transport.

Te has drawn many interest due to the excellent electrical and optical performances in both bulk and 2D scale. Although amorphous phase usually generates some particular characteristics, relevant studies are still inadequate. By using ab initio molecular dynamics (AIMD) simulations, we have explored the dynamics and structure of Te during amorphization process. The large fraction of 2- and 3-coordinated Te results in an average coordination number of 2.43 in amorphous Te (a-Te), deviating from the “8-N rule”. The 2-coordinated chain structures and the 3- and 4-coordinated defective octahedral clusters, together with 25.3% voids, make a-Te a flexible and fragile glass. As a result, a mid-gap state is observed in the electronic density of states. Our study deepens the insight on a-Te, which is useful for the design of novel electronic and optical devices.

Effects of alkaline earth metal atoms doping in boron hydrides at high pressure are investigated by first-principles calculations. The calculated results showed that doping with Mg, Ca, Ba, and Sr in B8H16 at 50 GPa is thermodynamically favorable and dynamically stable. The doping changes the B8H16 from a semiconductor to a metal with substantial electronic density-of-state around the Fermi level. The superconductivity of the alkaline earth metal doped B8H16 is studied based on electron-phonon coupling mechanism. The calculated critical superconducting transition temperatures (Tc) range from 10 to 25 K at 50 GPa upon doping. These results suggest that doping metal atoms in boron hydrides is an efficient way in designing superconducting materials.

The durability of the La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-δ (LSGM) electrolyte decreases when the Sm 0.5 Sr 0.5 Co 3-δ (SSC) is used as the cathode. In this study, we developed five types of cathode [Pt, Au, SSC (annealed at 800 and 1200 °C, denoted SSC-800, SSC-1200, respectively), pelleted SSC, and SSC with a Sm 0.2 Ce 0.8 O 1.9 (SDC) interlayer] to understand why the durability of LSGM in the presence of an SSC cathode declines. We found that, after constant polarization tests, the microstructure and cathodic polarization resistances of the Pt, SSC-800, SSC-1200 and SSC-pellet cathodes had changed, and the similar substances had separated from the crystalline grains at the grain boundaries, because of elemental interdiffusion at the interface. Hence, an SDC interlayer method was used to prevent the interdiffusion between the SSC cathode and the LSGM electrolyte. Consequently, the SDC interlayer is an effective method to prevent interdiffusion.

AC loss is an unavoidable problem for a conduction-cooled HTS superconducting magnetic energy storage (SMES) magnet during dynamic operation, which may cause a temperature raise and affect the reliable operation of the magnet. In this paper, the anisotropic homogenization method is employed to realize the modeling of a 150 kJ hybrid SMES magnet based on H-formulation. The SMES magnet has a maximum of approximately 7000 turns. First, the homogenization method is validated that it can reasonably predict the ac losses of both YBCCO coils and BSCCO coils, but it has lower accuracy to estimate the ac losses of BSCCO coils than YBCO coils. Then, ac loss characteristics of the SMES magnet during dynamic operations are investigated. The magnetic field, current density distribution, and ac loss distribution are presented and discussed for different operation conductions. The results indicate that a steady-state current of less than 100 A may be an appropriate choice during power exchange for reducing ac loss.

For automatic quench protection system, correction of quench judgment is important to the prolonged stable operation of superconducting devices. In poor electromagnetic environment, quench detection based on electrometric method is easily interfered by noise and severely disrupted quench signal may cause wrong quench determination and malfunction of quench protection, thereby resulting in unnecessary loss. One reason causing noise is current fluctuation and the noise is hard to be filtered by conventional filter circuit. In order to restrain noise and reduce false action of quench detection, this paper proposes a real-time wavelet analysis algorithm based on field programmable gate array platform. Experiment of filtering noise coupled whit quench signal of a HTS coil shows that the real-time wavelet analysis algorithm can filter noise out effectively. This method can be applied for filtering noise of quench detection for HTS coil and magnet.

The novel of iron, nickel and nitrogen doped carbon nanofibers (Fe/Ni-N-CNFs) as bifunctional electrocatalysts are prepared by electrospinning technique. In alkaline media, the Fe/Ni-N-CNFs catalysts (especially for Fe1Ni1-N-CNFs) exhibit remarkable electrocatalytic performances of oxygen reduction reaction (ORR)/oxygen evolution reaction (OER). For ORR catalytic activity, Fe1Ni1-N-CNFs catalyst offers a higher onset potential of 0.903 V, a similar four-electron reaction pathway, and excellent stability. For OER catalytic activity, Fe1Ni1-N-CNFs catalyst possesses a lower onset potential of 1.528 V and a smaller charge transfer resistance of 48.14 Ω. The unparalleled catalytic activity of ORR and OER for the Fe1Ni1-N-CNFs is attributed to the 3D porous cross-linked microstructures of carbon nanofibers with Fe/Ni alloy, N dopant, and abundant M-N x and NiOOH as catalytic active sites. Thus, Fe1Ni1-N-CNFs catalyst can be acted as one of the efficient and inexpensive catalysts of metal-air batteries.

Adsorption of Cadmium (Cd) on pristine and defective graphenes, including Stone–Wales (SW) defect and single vacancy (SV) defect, was studied by first-principles calculations. It is found that Cd adatom is weakly adsorbed on the pristine and SW defective graphene, while SV defect shows a substantial increase in the bonding with Cd adatom. Analysis of electronic density-of-state indicates that the effect of SV defect on the adsorption process can be mainly ascribed to the hybridisation between C-2p and Cd-5s orbitals. The results of charge density changes due to the Cd adsorption show the substantial amount of electrons are transferred from Cd to graphene, and the magnetic moment of substrate is increased after the adsorption of Cd. These experimental results suggest that SV graphene could be a good sensor for the detection of heavy metal ions.

The structural ordering at solid-liquid interfaces far from equilibrium is studied with molecular dynamics simulations for the Al-Sm system. Using the van-Hove self-correlation function as the criterion to identify attachment/detachment events that occur at the interface, we are able to determine the time-dependent interface position, and characterize the detailed interfacial structure ordering surrounding the attached atoms. For the interface between an undercooled Al 90 Sm 10 liquid and a metastable cubic structure, the solid induces the crystalline order of the cubic phase in the liquid layers, promoting the continuous growth of the crystal phase. When the same liquid is put in contact with f.c.c. Al, Sm from the liquid can still attach to the solid interface despite its insolubility in the Al lattice. Non-f.c.c. order is revealed surrounding the attached Sm atoms. We show that the local structure ordering at interface is highly correlated to solid packing and liquid ordering.

By analyzing Fe-Ni-B compositional diagram we predict an energetically and dynamically stable FeNiB2 compound. This system belongs to the class of highly responsive state of material, as it is very sensitive to the external perturbations. This state is also characterized by a high level of spin fluctuations which strongly influence possible magnetic long- and short-range orders. Furthermore, we demonstrate that these antiferromagnetically dominating fluctuations could lead to the appearance of spin mediated superconductivity. The obtained results suggest a promising avenue for the search of strong spin fluctuation systems and related superconductors.

The onset of ferromagnetism in cobalt-tin alloys is investigated experimentally and theoretically. The $\mathrm{C}{\mathrm{o}}_{1+x}\mathrm{Sn}$ alloys were prepared by rapid quenching from the melt and form a modified hexagonal NiAs-type crystal structure for $0.45\ensuremath{\le}x\ensuremath{\le}1$. The magnetic behavior is described analytically and by density-functional theory using supercells and the coherent-potential approximation. The excess of Co concentration $x$, which enters the interstitial $2d$ sites in the hypothetical NiAs-ordered parent alloy CoSn, yields a Griffiths-like phase and, above a quantum critical point $({x}_{c}\ensuremath{\approx}0.65)$, a quantum phase transition to ferromagnetic order. Quantum critical exponents are determined on the paramagnetic and ferromagnetic sides of the transition and related to the nature of the magnetism in itinerant systems with different types of chemical disorder.

We propose an approach that is under the framework of Gutzwiller wave function but goes beyond the commonly adopted Gutzwiller approximation to improve the accuracy and flexibility in treating the correlation effects. Detailed formalism is described for a dimer which is straightforwardly generalized later to more complicated periodic bulk systems. The accuracy of the approach is demonstrated by evaluating the potential energy curves of spin-singlet N2 dimer, spin-triplet O2 dimer, and 1D hydrogen chain. The computational workload of the approach can be easily handled by efficient parallel computing.

We report benchmark calculations of the correlation matrix renormalization (CMR) approach for 23 molecules in the well-established G2 molecule set. This subset represents molecules with spin-singlet ground state in a variety of chemical bonding and coordination environments. The QUAsi-atomic minimal basis-set orbitals (QUAMBOs) are used as local orbitals in both CMR and full configuration interaction (FCI) calculations for comparison. The results obtained from the calculations are also compared with available experimental data. It is shown that the CMR method produces binding and dissociation energy curves in good agreement with the QUAMBO-FCI calculations as well as experimental results. The CMR benchmark calculations yield a standard deviation of 0.09 A for the equilibrium bond length and 0.018 Hartree/atom for the formation energy, with a gain of great computational efficiency which scales like Hartree-Fock method.

Topology-protected surface transport of ultimate thinness in three-dimensional topological insulators (TIs) is breaking new ground in quantum science and technology. Yet a challenge remains on how to disentangle and selectively control surface helical spin transport from the bulk contribution. Here we use the mid-infrared and terahertz (THz) photoexcitation of exclusive intraband transitions to enable ultrafast manipulation of surface THz conductivity in Bi2Se3. The unique, transient electronic state is characterized by frequency-dependent carrier relaxations that directly distinguish the faster surface channel than the bulk with no complication from interband excitations or need for reduced bulk doping. We determine the topological enhancement ratio between bulk and surface scattering rates, i.e., γBS/γSS ~3.80 in equilibrium. The ultra-broadband, wavelength-selective pumping may be applied to emerging topological semimetals for separation and control of the protected transport connected with the Weyl nodes from other bulk bands., It remains challenging on how to selectively control terahertz conductivity at surface from the bulk contribution in topological insulators. Here, Luo et al. discover and manipulate topologically enhanced surface transport due to helical spin structure using mid-infrared and terahertz ultrafast photoexcitations.