Angell plot from the potential energy landscape perspective

Within the scenario of the potential energy landscape (PEL), a thermodynamic model has been developed to uncover the physics behind the Angell plot. In our model, by separating the barrier distribution in PELs into a Gaussian-like and a power-law form, we obtain a general relationship between the relaxation time and the temperature. The wide range of the experimental data in the Angell plot, as well as the molecular-dynamics data, can be excellently fitted by two characteristic parameters, the effective barrier (ω) and the effective width (σ) of a Gaussian-like distribution. More importantly, the fitted ω and σ^{2} for all glasses are found to have a simple linear relationship within a very narrow band, and fragile and strong glasses are well separated in the ω-σ^{2} plot, which indicates that glassy states appear only in a specific region of the PEL.

PASP: Property analysis and simulation package for materials

We have developed a software package, namely, PASP (Property Analysis and Simulation Package for materials), to analyze the structural, electronic, magnetic, and thermodynamic properties of complex condensed matter systems. Our package integrates several functionalities including symmetry analysis, global structure searching methods, effective Hamiltonian methods, and Monte Carlo simulation methods. In conjunction with first-principles calculations, PASP has been successfully applied to diverse physical systems. In this paper, we give a brief introduction to its main features and underlying theoretical formulism. Some typical applications are provided to demonstrate the usefulness, high efficiency, and reliability of PASP. We expect that further developments will make PASP a general-purpose tool for material simulation and property calculation of condensed matters.

Two-Dimensional SiS Layers with Promising Electronic and Optoelectronic Properties: Theoretical Prediction

Two-dimensional (2D) semiconductors can be very useful for novel electronic and optoelectronic applications because of their good material properties. However, all current 2D materials have shortcomings that limit their performance. As a result, new 2D materials are highly desirable. Using atomic transmutation and differential evolution global optimization methods, we identified two group IV-VI 2D materials, Pma2-SiS and silicene sulfide. Pma2-SiS is found to be both chemically, energetically, and thermally stable. Most importantly, Pma2-SiS has shown good electronic and optoelectronic properties, including direct bandgaps suitable for solar cells, good mobility for nanoelectronics, good flexibility of property tuning by layer control and applied strain, and good air stability as well. Therefore, Pma2-SiS is expected to be a promising 2D material in the field of 2D electronics and optoelectronics. The designing principles demonstrated in identifying these two tantalizing examples have great potential to accelerate the finding of new functional 2D materials.

Lattice-distortion Induced Magnetic Transition from Low-temperature Antiferromagnetism to High-temperature Ferrimagnetism in Double Perovskites A2FeOsO6 (A = Ca, Sr)

High-temperature insulating ferrimagnetism is investigated in order to further reveal its physical mechanisms, as well as identify potentially important scientific and practical applications relative to spintronics. For example, double perovskites such as Sr₂FeOsO₆ and Ca₂FeOsO₆ are shown to have puzzling magnetic properties. The former is a low-temperature antiferromagnet while the latter is a high-temperature insulating ferrimagnet. In order to understand the underlying mechanisms, we have investigated the frustrated magnetism of A₂FeOsO₆ by employing density functional theory and maximally-localized Wannier functions. We find lattice distortion enhances the antiferromagnetic nearest-neighboring Fe-O-Os interaction, however weakens the antiferromagnetic interactions via the Os-O-O-Os and Fe-O-Os-O-Fe paths, so is therefore responsible for the magnetic transition from the low-temperature antiferromagnetism to the high-temperature ferrimagnetism as the decrease of the A²⁺ ion radii. Also discussed is the 5d³-3d⁵ superexchange. We propose that such superexchange is intrinsically antiferromagnetic instead of ferromagnetic as previously thought. Our work clearly illustrates the magnetic frustration can be effectively relieved by lattice distortion, thus paving the way for tuning of complex magnetism in yet other 3d–5d (4d) double perovskites.

Self-regulation mechanism for charged point defects in hybrid halide perovskites

Hybrid halide perovskites such as methylammonium lead iodide (CH3NH3PbI3) exhibit unusually low free-carrier concentrations despite being processed at low-temperatures from solution. We demonstrate, through quantum mechanical calculations, that an origin of this phenomenon is a prevalence of ionic over electronic disorder in stoichiometric materials. Schottky defect formation provides a mechanism to self-regulate the concentration of charge carriers through ionic compensation of charged point defects. The equilibrium charged vacancy concentration is predicted to exceed 0.4% at room temperature. This behavior, which goes against established defect conventions for inorganic semiconductors, has implications for photovoltaic performance.

What are grain boundary structures in graphene?

We have developed a new global optimization method for the determination of the interface structure based on the differential evolution algorithm. Here, we applied this method to search for the ground state atomic structures of the grain boundary (GB) between armchair and zigzag oriented graphene. We find two new grain boundary structures with a considerably lower formation energy of about 1 eV nm(-1) than those of the previously widely used structural models. We also systematically investigate the symmetric GBs with the GB angle ranging from 0° to 60°, and find some new GB structures. Surprisingly, for an intermediate GB angle, the formation energy does not depend monotonically on the defect concentration. We also discovered an interesting linear relationship between the GB density and the GB angle. Our new method provides an important novel route for the determination of GB structures and other interface structures, and our comprehensive study on GB structures could provide new structural information and guidelines to this area.

Measurement of an enhanced superconducting phase and a pronounced anisotropy of the energy gap of a strained FeSe single layer in FeSe/Nb:SrTiO3/KTaO3 heterostructures using photoemission spectroscopy

Single-layer FeSe films with an extremely expanded in-plane lattice constant of 3.99±0.02  Å are fabricated by epitaxially growing FeSe/Nb:SrTiO3/KTaO3 heterostructures and studied by in situ angle-resolved photoemission spectroscopy. Two elliptical electron pockets at the Brillouin zone corner are resolved with negligible hybridization between them, indicating that the symmetry of the low-energy electronic structure remains intact as a freestanding single-layer FeSe, although it is on a substrate. The superconducting gap closes at a record high temperature of 70 K for the iron-based superconductors. Intriguingly, the superconducting gap distribution is anisotropic but nodeless around the electron pockets, with minima at the crossings of the two pockets. Our results place strong constraints on current theories.

Effect of surgery treatment on hypersplenism caused by cirrhotic portal hypertension

AIM

Aim of the study was to summarize the types and quantities of peripheral hematocytopenia in the patients of hypersplenism caused by cirrhotic portal hypertension and investigate the effect of surgery, including splenectomy on the patient's peripheral blood cells and liver function.

METHODS

The quantities of peripheral blood cells in the 322 patients of hypersplenism, caused by cirrhotic portal hypertension, were retrospectively studied. Then, the preoperative and postoperative values of peripheral blood cells and liver function were compared in 266 patients who were followed up. The liver function was scored and graded according to Child-Pugh scoring system.

RESULTS

The study enrolled 322 patients who showed hematocytopenia, including multi-hemocyte decrease in 206 patients (64%) and simple hemocyte decrease in 116 patients (36%). After surgical treatment in the 226 patients who were followed up, the quantities of peripheral blood cells significantly increased (P<0.01), Child-Pugh grade A increased by 32 patients (14.2%), while Child-Pugh grade C increased only by 2 patients (0.9%), the liver function scores decreased (P<0.05).

CONCLUSION

Hypersplenism caused by cirrhotic portal hypertension mainly manifests as a multi-hemocyte decrease and rarely shows single types of hematocytopenia. Surgical intervention including splenectomy can increase the reduction of hemocytes and promote the recovery of liver function.

Towards direct-gap silicon phases by the inverse band structure design approach

Diamond silicon (Si) is the leading material in the current solar cell market. However, diamond Si is an indirect band gap semiconductor with a large energy difference (2.3 eV) between the direct gap and the indirect gap, which makes it an inefficient absorber of light. In this work, we develop a novel inverse band structure design approach based on the particle swarming optimization algorithm to predict the metastable Si phases with better optical properties than diamond Si. Using our new method, we predict a cubic Si(20) phase with quasidirect gaps of 1.55 eV, which is a promising candidate for making thin-film solar cells.

Size-dependent melting behavior of iron nanoparticles by replica exchange molecular dynamics

Using the replica-exchange molecular dynamics method (REMD), we have investigated the size dependence of the melting behavior of iron nanoparticles. Comparing to conventional molecular dynamics (MD), the REMD method is found to be very efficient in determining the melting point by avoiding superheating and undercooling phenomena. With accurate determination of the melting point, we find that the melting temperature does not follow linearly with the inverse of size. By incorporating the size dependent thickness of surface liquid layer which is observed in our simulation, we propose a revised liquid skin melting model to describe the size dependent melting temperature.

Strong Dzyaloshinskii-Moriya interaction and origin of ferroelectricity in Cu2OSeO3

By performing density functional calculations, we investigate the origin of the Skyrmion state and ferroelectricity in Cu2OSeO3. We find that the Dzyaloshinskii-Moriya interactions between the two different kinds of Cu ions are extremely strong and induce the helical ground state and the Skyrmion state in the absence and presence of a magnetic field, respectively. On the basis of the general model for the spin-order induced polarization, we propose that the ferroelectric polarization of Cu2OSeO3 in the collinear ferrimagnetic state arises from an unusual mechanism, i.e., the single-spin-site contribution due to the spin-orbit coupling.

Strain effect on the diffusion of interstitial Mn in GaAs

The influence of external strain on the diffusion barriers of interstitial Mn in GaAs is studied using the first-principles calculations within the density functional theory. The diffusion barrier changes with strain in different manners: linear on the tensile strain and nonlinear on compressive strain, in contrast to the linear behavior of the continuum elastic model. The discrepancy between the continuum elastic model and the results of the first-principles method is attributed to the energy-level crossing caused by strain. Moreover, we find that the external strain can not only effectively change the diffusion barrier (even to zero, at certain strain), but also the position of saddle points along the migration path. Our finding provides an alternative way to reduce the population of interstitial Mn in GaAs, thus correspondingly to increase the Curie temperature of this system.

Giant ferroelectric polarization of CaMn7O12 induced by a combined effect of Dzyaloshinskii-Moriya interaction and exchange striction

By extending our general spin-current model to noncentrosymmetric spin dimers and performing density functional calculations, we investigate the causes for the helical magnetic order and the origin of the giant ferroelectric polarization of CaMn7O12. The giant ferroelectric polarization is proposed to be caused by the symmetric exchange striction due to the canting of the Mn4+ spin arising from its strong Dzyaloshinskii-Moriya interaction. Our study suggests that CaMn7O12 may exhibit a novel magnetoelectric coupling mechanism in which the magnitude of the polarization is governed by the exchange striction, but the direction of the polarization by the chirality of the helical magnetic order.

General theory for the ferroelectric polarization induced by spin-spiral order

The ferroelectric polarization of triangular-lattice antiferromagnets induced by helical spin-spiral order is not explained by any existing model of magnetic-order-driven ferroelectricity. We resolve this problem by developing a general theory for the ferroelectric polarization induced by spin-spiral order and then by evaluating the coefficients needed to specify the general theory on the basis of density functional calculations. Our theory correctly describes the ferroelectricity of triangular-lattice antiferromagnets driven by helical spin-spiral order and incorporates known models of magnetic-order-driven ferroelectricity as special cases.

Superhard Pseudocubic BC2N superlattices

It is currently under debate whether diamondlike BC2N may be harder than cubic BN (c-BN). Using the bond counting rule, we have performed an unconstrained search and identified a series of short period (111) superlattices that have much lower total energy than previously proposed structures. By examining the ideal strength of these pseudocubic boron-carbonitrides, we show that they are harder than c-BN. Our results are consistent with experimental findings, but in contrast with a recent theoretical study, which claimed that the BC2N is less hard than c-BN.

Sharp corners in the cross section of ultrathin Si nanowires

We have determined stable geometries for pristine Si nanowires grown along their 100 axis through systematic density functional studies. Strikingly, Si nanowires with diameters smaller than 1.7 nm prefer a shape that has a square cross section. This stems from dimerization between corner atoms and also from benign reconstruction patterns that maximally saturate Si dangling bonds.

First-principles study of interaction of cluster Au32 with CO, H2, and O2

First-principles calculations are performed to study the interaction of cluster Au(32) with small molecules, such as CO, H(2), and O(2). The cagelike Au(32)(I(h)) shows a higher chemical inertness than the amorphous Au(32)(C(1)) with respect to the interaction with small molecules CO, H(2), and O(2). H(2) can only be physically adsorbed on Au(32)(I(h)), while it can be dissociatively chemisorbed on Au(32)(C(1)). Although CO can be chemically adsorbed on Au(32)(I(h)) and Au(32)(C(1)) with one electron transferred from Au(32) to the antibonding pi* orbit of CO, it is bound more strongly on Au(32)(C(1)) than on Au(32)(I(h)). Spin polarized and spin nonpolarized calculations result almost identical ground state structures of Au(32)(I(h))-O(2) and Au(32)(C(1))-O(2), in which O(2) is dissociatively chemisorbed.

Ab initio studies on the reaction of O2 with Ban (n=2,5) clusters

Ab initio theoretical calculations have been performed to study the reaction of O(2) with Ba(n) (n=2,5) clusters. Our results show that O(2) can easily chemisorb and dissociate on small Ba(n) clusters and there is no obvious energy barrier in the process of the dissociation. The local magnetic moment contributed by oxygen must vanish during the intermediate states before the O(2) dissociation. Correspondingly, local magnetic moment only decreases from 2 mu(B) to about 1 mu(B) if O(2) molecularly adsorbs onto Ba(5) cluster. The electronic structure analysis indicates that the charge transfer from Ba(n) cluster to O(2) as well as the orbital hybridization between the cluster and the oxygen molecule may play a key role in O(2) dissociation.

Surface mobility difference between Si and Ge and its effect on growth of SiGe alloy films and islands

Based on first-principles calculations of surface diffusion barriers, we show that on a compressive Ge(001) surface the diffusivity of Ge is 10(2)-10(3) times higher than that of Si in the temperature range of 300 to 900 K, while on a tensile surface, the two diffusivities are comparable. Consequently, the growth of a compressive SiGe film is rather different from that of a tensile film. The diffusion disparity between Si and Ge is also greatly enhanced on the strained Ge islands compared to that on the Ge wetting layer on Si(001), explaining the experimental observation of Si enrichment in the wetting layer relative to that in the islands.

First-principles studies on the reactions of O2 with silicon clusters

The reactions of an O(2) molecule with the neutral and positively charged Si(n)(n = 3-16) clusters are studied with first-principles calculations. Neutral Si(n)(n = 4,5,6,7,10,14) and charged Si(n) (+)(n = 4,5,6,7,13,15) clusters show higher inertness to O(2) molecule adsorption, which is in good agreement with experimental results. Both charge transfer and hybridizations between Si and O play an important role in the dissociative adsorption of O(2) molecule. We find that the spin triplet-single conversion of O(2) molecule is always accompanied with O(2) dissociatively chemisorbed on the Si(n) clusters.

Ab initio study on structural and electronic properties of BanOm clusters

Density-functional calculation within local density approximation, shows that the electronic property of a barium oxide cluster is strongly correlated with its equilibrium structure. The ground-state structures of BanOm (4 < or = n < or = 9,m < or = n) clusters can be classified into four categories: (a) compact, (b) dangling state, (c) F-center, and (d) stoichiometric. The compact cluster is metallic, almost no energy gap exists between the highest occupied and the lowest unoccupied molecular orbitals. The energy gap for the dangling state cluster is larger than that for the F-center cluster, while the stoichiometric cluster has the largest energy gap.

Oxidation of carbon nanotubes by singlet O2

Chemisorption of singlet (1)Delta(g) O2 on single-walled carbon nanotubes is reexamined by first principles calculations, and the reaction barrier is substantially lower than previously reported when the spin on O2 is correctly treated. The process is initiated by the cycloaddition of a singlet O2 on top of a C-C bond and ended with an epoxy structure with each of the two oxygen atoms occupying a bridge position. The overall process is exothermic, with an activation barrier as low as 0.61 eV for the (8, 0) tube. Our results raise the possibility that carbon nanotubes with small diameters could be degraded after exposure to air and sunlight, similar to the degradation of natural rubber and synthetic plastics.

Chemisorption of hydrogen molecules on carbon nanotubes under high pressure

Based on first principles calculations, we propose a mechanism for the dissociative chemisorption of H2 on carbon nanotubes. The breaking of the H--H bond is concerted with the formation of two C--H bonds on two adjacent carbon nanotubes in solid phase, facilitated by the application of high pressure which shortens the interstitial distance between nanotubes. The process is reversible upon the release of external pressure and could make an important contribution to the observed hydrogen storage capacity of carbon nanotubes. The previously unexplained experimental observations of the direct hydrogenation of fullerenes under high pressure lend further support for such a mechanism.

[Progress in telomerase and the inhibitors]

In cells division chromosome length is shorten for the ending DNA couldn't be replicated completely, and the loss of telomere DNA will lead to senescence and death. Activation of telomerase can elongate telomere length and maintain gene stability. Up-regulation of telomerase is considered to be responsible for immortalization and carcinogenesis. It plays an important role in cell-span and cell division. The telomerase inhibitors will become efficient drugs in tumor therapy.

[Development of the portable blood glucose meter]

This article introduces the research work on blood glucose assay instrument. It uses the method that immobilizes enzyme on nylon66 film and detects resultant color by photo-electric sensor The detecting range is 0-30 mml/L and the detecting time is 50 s.

Efficiency of generalized simulated annealing

We have explored the evolution of the efficiency of generalized simulated annealing (GSA) through a comparative study with classical simulated annealing (CSA) and fast simulated annealing (FSA). Our calculations on the Thomson model and nickel clusters show that the relative efficiency of GSA compared to CSA and FSA increases with the number of variables of the objective function. Thus, relative to CSA and FSA, the more complex the system, the more efficient is the GSA method.