Role of hot electron transport in scintillators: A theoretical study

Despite recent intensive study on scintillators, several fundamental questions on scintillator properties are still unknown. In this work, we use ab‐initio calculations to determine the energy dependent group velocity of the hot electrons from the electronic structures of several typical scintillators. Based on the calculated group velocities and optical phonon frequencies, a Monte‐Carlo simulation of hot electron transport in scintillators is carried out to calculate the thermalization time and diffusion range in selected scintillators. Our simulations provide physical insights on a recent trend of improved proportionality and light yield from mixed halide scintillators. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Do surfaces of positive electrostatic potential on different halogen derivatives in molecules attract? like attracting like!

Coulomb's law states that like charges repel, and unlike charges attract. However, it has recently been theoretically revealed that two similarly charged conducting spheres will almost always attract each other when both are in close proximity. Using multiscale first principles calculations, we illustrate practical examples of several intermolecular complexes that are formed by the consequences of attraction between positive atomic sites of similar or dissimilar electrostatic surface potential on interacting molecules. The results of the quantum theory of atoms in molecules and symmetry adapted perturbation theory support the attraction between the positive sites, characterizing the F•••X (X = F, Cl, Br) intermolecular interactions in a series of 20 binary complexes as closed‐shell type, although the molecular electrostatic surface potential approach does not (a failure!). Dispersion that has an r⁻⁶ dependence, where r is the equilibrium distance of separation, is found to be the sole driving force pushing the two positive sites to attract. © 2017 Wiley Periodicals, Inc.     

Noncollinear magnetization density in VAu4

The spin and orbital magnetic moments of VAu₄ have been calculated using a first principles method that allows for noncollinear magnetic ordering. The large spin–orbit coupling of the Au atom is argued to induce large noncollinear components of the magnetization density as well as a parallel coupling between spin and orbital moments of the V atom, in contrast to expectations from Hund's third rule. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

The effect of impurities Pb,Bi, and PbO on erosion properties of Lead-Bismuth Eutectic alloy on Fe3O4 oxide film by first principle calculations

The first-principle calculation was performed to study the effect of impurities Pb, Bi, and PbO on erosion properties of liquid lead-bismuth eutectic alloy on the metal oxide (Fe₃O₄) and its surfaces. We found that whether in the bulk or on the surface of Fe₃O₄ the formation energy by substitution of Fe with Bi is slightly larger than that with Pb substitution and the formation energy by substitution of Fe with PbO is much larger than those with Pb and Bi, indicating that PbO has weaker corrosion potential than Pb/Bi. The calculation results show that a tetrahedral site in Fe₃O₄ should be the weakest position where Fe₃O₄ is attacked by these exotic impurities. The corrosion process on the oxide film will be initialized at that position. It can be seen that for the doping case the dissociation energy of Fe atom in the (110) surface has the smallest value, a medium value in (100) surface, and the largest value in (111) surface. Correspondingly, the corrosion resistance of doping Fe₃O₄ film in (110) surface is the weakest one among these surfaces. For the doping-free case, the (100) surface has the weakest corrosion resistance. By comparing the doping case with no-doping case it can be seen that the impurities of Pb, Bi, and PbO will weaken the corrosion resistance of Fe₃O₄ film further. The doping has a negative impact on the stability of the structure and on the corrosion resistance of Fe₃O₄ film. From present results, it is also seen that the replacement of Fe in Fe₃O₄ by multiple impurities is more likely to occur than the replacement of only single impurity.     

Van der Waals Effects on semiconductor clusters

Van der Waals (vdW) interactions play an important role on semiconductors in nanoscale. Here, we utilized first‐principles calculations based on density functional theory to demonstrate the growth mode transition from prolate to multiunit configurations for Ge_n (n = 10–50) clusters. In agreement with the injected ion drift tube techniques that “clusters with n < 70 can be thought of as loosely bound assemblies of small strongly bound fragments (such as Ge₇ and Ge₁₀),” we found these stable fragments are connected by Ge₆, Ge₉, or Ge₁₀ unit (from bulk diamond), via strong covalent bonds. Our calculated cations usually fragment to Ge₇ and Ge₁₀ clusters, in accordance with the experiment results that the spectra Ge₇ and Ge₁₀ correspond to the mass abundance spectra. By controlling a germanium cluster with vdW interactions parameters in the program or not, we found that the vdW effects strengthen the covalent bond from different units more strikingly than that in a single unit. With more bonds between units than the threadlike structures, the multiunit structures have larger vdW energies, explaining why the isolated nanowires are harder to produce. © 2015 Wiley Periodicals, Inc.     

On Material Equations in Second Gradient Electroelasticity

The concern of this work is the derivation of material conservation and balance laws for second gradient electroelasticity. The conservation laws of material momentum, material angular momentum and scalar moment of momentum on the material manifold are derived using Noether's theorem and the exact conditions under which they hold are rigorously studied. The corresponding balance laws are also presented. This revised version was published online in June 2006 with corrections to the Cover Date.     

金属修饰Ti_2N MXene吸附分解H_2S的第一性原理计算

通过第一性原理计算研究了Ti_2NO_2 MXene对H_2S的吸附、分解行为. Ti_2NO_2对H_2S气体分子的吸附结果表明,两者之间为弱的物理吸附, Ti_2NO_2无法有效吸附H_2S气体.采用过渡金属(Sc、 V)修饰Ti_2NO_2的研究结果表明,Sc和V可以在Ti_2NO_2表面上稳定存在,不易发生团聚,其最稳定吸附位为N原子上方.进一步研究了Sc、 V修饰的Ti_2NO_2对H_2S气体分子的吸附行为,结果表明金属修饰后其吸附H_2S的能力明显提高.此外还发现, H_2S分子可以在Sc/Ti_2NO_2和V/Ti_2NO_2表面直接解离为HS*和H*,而后HS*中的H原子再与H*进一步结合形成H_2, S原子则与过渡金属成键. HS*在V/Ti_2NO_2表面解离的势垒为1.69 eV,低于在Sc/Ti_2NO_2表面的2.08 eV,表明V/Ti_2NO_2有望成为吸附、分解H_2S气体的理想候选材料.     

Comparative analysis of essential oils from eight herbal medicines with pungent flavor and cool nature by GC–MS and chemometric resolution methods

Systematic comparative research was conducted on essential oils from eight traditional Chinese medicines (TCM) of pungent flavor and cool nature because the essential oils are the main active ingredients of herbs of this kind. The work was based on their component analysis by gas chromatography–mass spectrometry (GC–MS), on their retention indices, as well as on chemometric resolution methods. A total of 144 compounds were tentatively identified, accounting for 69.0% to 91.8% of the total essential oils. It is worth noting that there are 67 compounds in at least three of these eight essential oils. Moreover, many biologically active compounds, such as hexanal, α‐pinene, camphene, β‐pinene, p‐cymene, limonene, eucalyptol, (Z)‐ocimene, γ‐terpinene, camphor, p‐menthone, 4‐terpineol, α‐terpineol, carvone, eugenol, caryophyllene, β‐farnesene, α‐curcumene, β‐selinene, δ‐cadinene, caryophyllene oxide, cedrol, n‐hexadecanoic acid, benzaldehyde, benzeneacetaldehyde, phthalic acid diisobutyl ester, linoleic acid, tetradecanoic acid, (Z,Z,Z)‐9,12,15‐octadecatrienoic acid, eucalyptol, pentadecanoic acid, hexadecanoic acid methyl ester, linoleic acid methyl ester, exist in at least four of the eight essential oils. These results might help us to understand why the eight herbs are all of pungent flavor and cool nature according to the theory of TCM, and may provide a useful chemical basis for future research on herbs of this kind.