Electronic structures and optical properties of Ⅲ_A-doped wurtzite Mg_(0.25)Zn_(0.75)O

The energy band structures, density of states, and optical properties of IIIA-doped wurtzite Mg0.25Zn0.75O(IIIA= Al,Ga, In) are investigated by a first-principles method based on the density functional theory. The calculated results show that the optical bandgaps of Mg0.25Zn0.75O:IIIAare larger than those of Mg0.25Zn0.75 O because of the Burstein–Moss effect and the bandgap renormalization effect. The electron effective mass values of Mg0.25Zn0.75O:IIIAare heavier than those of Mg0.25Zn0.75 O, which is in agreement with the previous experimental result. The formation energies of MgZnO:Al and MgZnO:Ga are smaller than that of MgZnO:In, while their optical bandgaps are larger, so MgZnO:Al and MgZnO:Ga are suitable to be fabricated and used as transparent conductive oxide films in the ultra-violet(UV) and deep UV optoelectronic devices.     

Molecular Dynamics Study of the Structural Modification of Porous Silica from Low-Energy Recoils

Molecular dynamics simulations are performed to investigate the effects of low-energy recoils on the microscopic structure of porous silica. Exhibiting a logistic growth with the recoil energy, the displacement probability of Si is shown to be smaller than that of O at the same primary knock-on level. Computations of pair distribution functions and bond angle distributions reveal that this material upon irradiation with energies around the displacement thresholds mainly undergoes structural changes in the medium-range order. In the porous network,while the formation of nonbridging oxygen defects tends to induce shorter Si–O bonds than those formed by bridging oxygen atoms, a remarkable increase of inter-tetrahedral bond angles created by multiple recoils can be observed and associated with the rearrangement of ring statistics.     

Electron density distribution of LiMn_2O_4 cathode investigated by synchrotron powder x-ray diffraction

Electron density plays an important role in determining the properties of functional materials. Revealing the electron density distribution experimentally in real space can help to tune the properties of materials. Spinel Li Mn2 O4 is one of the most promising cathode candidates because of its high voltage, low cost, and non-toxicity, but suffers severe capacity fading during electrochemical cycling due to the Mn dissolution. Real-space measurement of electron distribution of Li Mn2 O4 experimentally can provide direct evaluation on the strength of Mn–O bond and give an explanation of the structure stability.Here, through high energy synchrotron powder x-ray diffraction(SPXRD), accurate electron density distribution in spinel Li Mn2 O4 has been investigated based on the multipole model. The electron accumulation between Mn and O atoms in deformation density map indicates the shared interaction of Mn–O bond. The quantitative topological analysis at bond critical points shows that the Mn–O bond is relatively weak covalent interaction due to the oxygen loss. These findings suggest that oxygen stoichiometry is the key factor for preventing the Mn dissolution and capacity fading.     

Interfacial potential approach for Ag/ZnO （0001） interfaces

Systematic approaches are presented to extract the interfacial potentials from the ab initio adhesive energy of the interface system by using the Chen–M ¨obius inversion method. We focus on the interface structure of the metal（111）/Zn O（0001）in this work. The interfacial potentials of Ag–Zn and Ag–O are obtained. These potentials can be used to solve some problems about Ag/Zn O interfacial structure. Three metastable interfacial structures are investigated in order to check these potentials. Using the interfacial potentials we study the procedure of interface fracture in the Ag/Zn O（0001） interface and discuss the change of the energy, stress, and atomic structures in tensile process. The result indicates that the exact misfit dislocation reduces the total energy and softens the fracture process. Meanwhile, the formation and mobility of the vacancy near the interface are observed.     

Effect of P impurity on NiAlΣ5 grain boundary from first-principles study

First-principles calculations based on the density functional theory(DFT) and ultra-soft pseudopotential are employed to study the atomic configuration and charge density of impurity P in Ni Al Σ5 grain boundary(GB). The negative segregation energy of a P atom proves that a P atom can easily segregate in the Ni Al GB. The atomic configuration and formation energy of the P atom in the Ni Al GB demonstrate that the P atom tends to occupy an interstitial site or substitute a Al atom depending on the Ni/Al atoms ratio. The P atom is preferable to staying in the Ni-rich environment in the Ni Al GB forming P–Ni bonds. Both of the charge density and the deformation charge imply that a P atom is more likely to bond with Ni atoms rather than with Al atoms. The density of states further exhibits the interactions between P atom and Ni atom, and the orbital electrons of P, Ni and Al atoms all contribute to P–Ni bonds in the Ni Al GB. It is worth noting that the P–Ni covalent bonds might embrittle the Ni Al GB and weakens the plasticity of the Ni Al intermetallics.     

Energy dependence on the electric activities of a neuron

A nonlinear circuit can be designed by using inductor, resistor, capacitor and other electric devices, and the electromagnetic field energy can be released from the circuit in the oscillating state. The generation of spikes or bursting states in neurons could be energetically a costly process. Based on the Helmholtz's theorem, a Hamilton energy function is defined to detect the energy shift induced by transition of electric modes in a Hindmarsh–Rose neuron. It is found that the energy storage is dependent on the external forcing, and energy release is associated with the electric mode. As a result, the bursting state and chaotic state could be helpful to release the energy in the neuron quickly.     

Terahertz radiation from pentacene organic diode at room temperature

We investigate terahertz radiation(T-rays) from a pentacene organic diode at room temperature. The quantum chemistry calculation for frequency-related Huang–Rhys factor of pentacene is also carried out. The results demonstrate that the T-rays can come from a bending vibration of pentacene skeleton after the energy of pentacene exciton transferring to the vibrational excited state via electron–phonon coupling. Frequency and natural bond orbital analytics of pentacene and its derivatives are performed in order to explain the result and develop new materials to get higher emission. This work provides a new way to produce T-rays with a simple device at room temperature.     

Effects of Grain Boundary Characteristics on Its Capability to Trap Point Defects in Tungsten

As recombination centers of vacancies(Vs) and self-interstitial atoms(SIAs), firstly grain boundaries(GBs)should have strong capability of trapping point defects. In this study, abilities to trap Vs and SIAs of eight symmetric tilt GBs in tungsten are investigated through first-principles calculations. On the one hand, vacancy formation energy E~f_V rapidly increases then slowly decreases as the hard-sphere radius r_0 of the vacancy increases.The value of E~f_V is the largest when r_0 is about 1.38 ?, which is half the distance between the nearest atoms in equilibrium single crystal tungsten. That is, any denser or looser atomic configuration around GBs than that in bulk is helpful to form a vacancy. On the other hand, SIA formation energy E~f_(SIA) at GBs decreases monotonically with increasing the hard-sphere radius of the interstitial sites, which indicates that GBs with larger interstitial sites have stronger ability to trap SIAs. Based on the data obtained for GBs investigated in this study, it is found that the ability to trap Vs increases as the GB energy increases, and the capability of trapping SIAs linearly increases as the excess volume of GB increases. Due to its lowest GB energy and smallest excess volume among all GBs studied, twin GB ∑3(110)[111] has the weakest capability to trap both Vs and SIAs.     

Self-Bound Quantum Droplet with Internal Stripe Structure in One-Dimensional Spin-Orbit-Coupled Bose Gas

We study the quantum-droplet state in a three-dimensional(3D) Bose gas in the presence of 1D spin-orbit coupling and Raman coupling, especially the stripe phase with density modulation, by numerically computing the ground state energy including the mean-field energy and Lee–Huang–Yang correction. In this droplet state,the stripe can exist in a wider range of Raman coupling, compared with the BEC-gas state. More intriguingly,both spin-orbit coupling and Raman coupling strengths can be used to tune the droplet density.     

Spin-star environment assisted entanglement generation in weakly coupled bipartite systems

We study the entanglement evolution in a weakly coupled bipartite system with a large energy level difference under the influence of spin-star environments. The subsystems can be coupled to a pure state or a thermal equilibrium state spin-star environment. Our results show that, in the case of the coupling strength being less than the energy level difference of the subsystems （weakly coupled）, the spin-star environment can always be used to assist the entanglement generation of the bipartite system.