NaB2和Na2B的结构与解析势能函数

使用Gaussian03程序包,采用单双取代耦合簇(CCSD)方法,选择基组6-311+g(2df)、6-311++g(3df,3pd)分别对B2及NaB和Na2分子的基态进行优化计算,运用最小二乘法拟合得到B2、NaB和Na2分子势能函数,给出与实验值符合很好的光谱常数;选择6-31++g（3df,3pd）基组,对NaB2和Na2B分子的结构进行优化计算.在此基础上,采用多体项展式法,得到NaB2和Na2B分子基态解析势能函数.势能面静态特征表明,该势能函数准确再现了NaB2和Na2B分子基态平衡结构.     

D+HS反应的含时量子动力学研究

利用含时波包方法对D+HS交换和抽取通道进行量子动力学研究,动力学计算中所采用的势能面由高精度从头算能量点构建.在平动能0.0～2.0 eV区间内计算了反应物初始振转基态时的总反应几率和积分反应截面,并且计算了初始振动激发态对积分反应截面的影响.所有动力学计算均考虑了科里奥利耦合效应.在低平动能时抽取通道在反应中占主导地位,而交换通道在高平动能时占主导地位.在整个所研究的平能能区间内,反应物HS的振动激发对抽取和交换通道反应都有增强作用.     

CL20-TNT共晶高温热解的ReaxFF/lg反应力场分子动力学模拟

ReaxFF/lg势函数是在ReaxFF的基础上增加了对范德华引力的描述, 因此可以更好地用于描述晶体密度和结构, 而含能材料密度很大程度上影响着爆轰的宏观性质(如爆速、反应区宽度、能量输出结构等). 本文采用ReaxFF/lg反应力场分析了高温条件下凝聚相CL20-TNT共晶的初始分解情况, 并通过简单的指数函数拟合势能演化曲线获得了平衡和诱导期以及整体反应时间, 随后通过反应速率方程得到了共晶热解的活化能E_a (185.052 kJ/mol). CL20-TNT共晶热解过程中CL20分子均在TNT之前分解完毕, 并且随着温度的升高, TNT的分解速率明显加快, 温度越高二者完全分解所需的时间越接近. 有限时间步长下的产物识别分析显示主要产物为NO₂, NO, CO₂, N₂, H₂O, HON, HNO₃. NO₂是C–NO₂和N–NO₂键均裂共同贡献的结果, 其产量快速地增加, 达到峰值后开始减少, 此过程伴随着NO₂参与其他反应使得NO₂中的N原子进入到其他的含N 分子中. 次要产物主要为CO, N₂O, N₂O₅, CHO. N₂O具有很强的氧化能力, 使其分布有着剧烈的波动特征. 关键词： 共晶结构 高温热解 ReaxFF/lg 势函数 分子动力学     

Mo,Ta, W在NixAl1-x(x=0.25,0.5,0.75) 中的择优占位

用多体势结合分子动力学计算了L1₂型NiAl₃, L1₂型Ni₃Al, L1₀型NiAl和B₂ 型NiAl的晶格常数, 结合能以及合金形成热; 分析了结构性点缺陷在上述四种合金中的存在形式; 在此基础上研究了合金化元素Mo, Ta, W在Ni_xAl_1-x(x=0.25,0.5,0.75)中的择优占位行为. 计算结果表明: 对于四种结构的Ni-Al合金, 偏离理想化学配比时,主要的结构缺陷形式是反位置; 根据占位能最小化, 第三组元元素Mo, Ta, W在上述四种Ni-Al中都显著优先占据Al格位. 关键词： 多体势 Ni-Al合金 占位     

182Os 核yrast带相继SU(3)–U(5)–SU(3)结构相变势能曲面的一种可能理解

基于联合实施微观相互作用玻色子模型的最大F旋方案 (sdIBM-F_max)与γ射线能量-自旋曲线 (γ-ray energy over spin curves, E-GOS)方案, 成功描述了¹⁸²Os核yrast带相继的SU(3)–U(5)–SU(3)结构相变, 由于缺少直观解释而显得抽象. 本文借助微观sdIBM-F_max的微观参数与Bohr哈密顿量的势能曲面方程之间存在的泛函关系, 几何地给出了对这种相继相变途径的另外一种可能理解; 并阐述了在完全变形核的高角动量态中, 由于量子效应在高激发态与低激发态之间生成高简并的临界区, 提供了γ振动能量会变得低于转动能量的一个可能途径, 从而实现了SU(3)–U(5)的相变. 关键词： yrast带结构演化 势能曲面 相变临界区 182Os核')" href="#">¹⁸²Os核     

硅熔化特性的分子动力学模拟–-不同势函数的对比研究

分别采用Stillinger-Weber (SW)势、修正的成熟原子嵌入模型(MEAM)势、 Tersoff势和HOEP (highly optimized empirical potential)势来描述硅原子间相互作用, 运用分子动力学方法对比模拟研究了四种势函数的硅晶体的体熔化和表面熔化特性. 结果表明: 四种势函数均能反映出硅的热膨胀、高温熔化和熔化时吸热收缩等基本物理规律. 但综合对比发现, Tersoff势和MEAM势相对更适合描述硅的熔化和凝固过程, SW势次之, HOEP势则不适合描述硅的熔化和凝固过程. 关键词： 硅 势函数 熔化 分子动力学     

电子辐照条件下初始电位对介质材料表面电位衰减特性的影响

为了研究航天器介质材料表面不同电位初始值对表面电位衰减特性的影响。利用航天器带电地面模拟实验设备对聚酰亚胺和聚四氟乙烯介质材料充电到不同电位值,然后关闭电子枪,用电位计测量介质材料表面电位的衰减曲线,并从理论上对cross-over现象进行分析。介质材料初始电位值越大,则表面电位衰减速度越快,且在一定的时间段内电位衰减效率随初始电位值的增大而变大;在相同的真空度条件下,对于初始电位值之和相等的两组衰减曲线,初始电位值之间差值较小的一组衰减曲线更容易出现cross-over现象;出现cross-over现象的时间和电子的迁移率相关,对于相同的两个初始电位,迁移率越大的材料则出现cross-over现象的时间越短,电位衰减会更快。航天器介质材料表面充电电位越大则衰减速度越快,在一定时间的衰减效率越高。     

Effect of the Addition of Lemongrass (Cymbopogon citratus) on the Quality and Microbiological Stability of Craft Wheat Beers

Lemongrass (Cymbopogon citratus) is a valuable source of vitamins, macro- and microelements, and essential oils. The purpose of this study was to compare the physicochemical properties, sensory properties, antioxidant activity, and microbiological stability of wheat beers enriched with varying additions of crushed lemongrass. Sensory evaluation showed that wheat beers enriched with 2.5% m/v lemongrass were characterised by balanced taste and aroma (overall impression). Physicochemical analysis of the wheat beers showed that increasing the concentration of lemongrass in the finished product negatively affected the ethanol content. Alcohol content in wheat beer enriched with 1% m/v lemongrass was on average 14.74% higher than wheat beer enriched with 2.5% m/v lemongrass and on average 17.93% higher than wheat beer enriched with 5% m/v addition of lemongrass. The concentration of lemongrass in the finished product also increased the acidity of the beers and affected the colour of the wheat beers compared to the control beer. The total polyphenol content and antioxidant activity of lemongrass-enriched wheat beers varied. Of the lemongrass-enriched beers analysed, the beer product with 5% m/v lemongrass was the most microbiologically stable. According to the study, crushed lemongrass-enriched wheat beer may represent a new trend in the brewing industry, but the brewing process still needs to be improved.     

HeH+ under Spatial Confinement

In the present study, the influence of spatial confinement on the bond length as well as dipole moment, polarizability and (hyper)polarizabilities of HeH+ ion was analyzed. The effect of spatial confinement was modelled by cylindrically symmetric harmonic oscillator potential, that can be used to mimic high pressure conditions. Based on the conducted research it was found that the spatial confinement significantly affects the investigated properties. Increasing the confinement strength leads to a substantial decrease of their values. This work may be of particular interest for astrochemistry as HeH+ is believed to be the first compound to form in the Universe.     

Quantum Mechanical Calculations of Redox Potentials of the Metal Clusters in Nitrogenase

We have calculated redox potentials of the two metal clusters in Mo-nitrogenase with quantum mechanical (QM) calculations. We employ an approach calibrated for iron–sulfur clusters with 1–4 Fe ions, involving QM-cluster calculations in continuum solvent and large QM systems (400–500 atoms), based on structures from combined QM and molecular mechanics (QM/MM) geometry optimisations. Calculations on the P-cluster show that we can reproduce the experimental redox potentials within 0.33 V. This is similar to the accuracy obtained for the smaller clusters, although two of the redox reactions involve also proton transfer. The calculated P¹⁺/P^N redox potential is nearly the same independently of whether P¹⁺ is protonated or deprotonated, explaining why redox titrations do not show any pH dependence. For the FeMo cluster, the calculations clearly show that the formal oxidation state of the cluster in the resting E₀ state is MoIIIFe3IIFe4III , in agreement with previous experimental studies and QM calculations. Moreover, the redox potentials of the first five E₀–E₄ states are nearly constant, as is expected if the electrons are delivered by the same site (the P-cluster). However, the redox potentials are insensitive to the formal oxidation states of the Fe ion (i.e., whether the added protons bind to sulfide or Fe ions). Finally, we show that the later (E₄–E₈) states of the reaction mechanism have redox potential that are more positive (i.e., more exothermic) than that of the E₀/E₁ couple.