金属间化合物Al~3Fe熔体结构的温度变化特性研究

利用分子动力学模拟技术,详细考察了在快速凝固条件下AL~3Fe熔体结构的温度变化特征。结果表明:Al~3Fe熔体中存在不同类型的原子基团.原子集团是以各种各样的键对和多面体的形式存在的.利用键对分析技术,计算出了不同温度下的键对类型数和二十面体的两类键取向序参数,分析了Al-Fe合金在快速凝固条件下非晶形成的演化特点。     

二十面体准晶对非晶形成影响的模拟

采用分子动力学模拟技术,以液态金属Ni为例,研究了在不同冷却条件下形成晶体及非晶的过程.模拟采用镶嵌原子法(EAM)作用势,得到了不同温度、不同冷却速度下Ni的径向分布函数以及原子组态变化的重要信息,利用键对分析技术探讨了二十面体准晶对非晶形成的影响.     

铁磁性物质Co的液态结构分子动力学模拟

用分子动力学模拟方法在１８７３－３００Ｋ的温度范围内对液态Ｃｏ的微正则系综进行了模拟研究,模拟采用ＥＡＭ相互作用势,对时间和空间的平均,得到了不同温度下Ｃｏ的双体分布函数及原子组态变化的重要信息,当冷却速度较慢时,液态金属Ｃｏ最终形成晶态,当冷却速度较快时,液态Ｃｏ最后形成了非晶态,双体分布函数随的变化规律说明液态金属随温度的降低,有序度不断增强,利用键对分析技术对模拟结果作了深入分析,液态金属中     

二元合金Ag_(50)Rh_(50)从液态到非晶的分子动力学计算

本文对贵重金属银铑合金Ag50Rh50的液态结构和激冷过程进行了分子动力学模拟研究原子间作用势采用紧束缚势模拟在施加了周期性边界条件的常压状态下进行。采用了偶关联函数、键对分析技术和键取向序参数以分子动力学模拟计算方法揭示了Ag50Rh50的液态结构存在原子偏聚特征以及在快速凝固过程形成原子偏聚的不均匀非晶并与同族过渡金属进行了非晶形成能力的比较。     

二元合金Ag50Rh50从液态到非晶的分子动力学计算

本文对贵重金属银铑合金Ag50Rh50的液态结构和激冷过程进行了分子动力学模拟研究,原子间作用势采用紧束缚势,模拟在施加了周期性边界折常压状态下进行。采用了偶关联函数,键对分析技术和键取向序参, 分子动力学模拟计算方法揭示了Ag50Rh50的液态结构存在原子偏聚特征以及在快速凝固过程形成原子偏聚的不均匀非晶,并与同族过渡金属进行了非晶形成能力的比较。     

贵金属Au的液态结构分子动力学模拟

用分子动力学模拟方法在1573－200K的温度范围内对液态Au的微正则系综进行了模拟研究。模拟采用或嵌原子相互作用势对时间和空间的平均，得到了不同温度下Au的润分布函数及原子组态变化的重要信息，并利用键对分析技术对模拟结果作了深入讨论．     

BaPbO3的生成及EXAFS研究

采用低Pb/Ba摩尔比及低的反应温度，以BaCO₃和PbO为原料，固相反应合成了BaPbO₃无机微粉。通过XRD分析，确定了不同Pb、Ba比例下生成的Ba-Pb-O化合物均为立方钙钛矿结构。首次采用EXAFS对BaPbO₃微粉中Pb原子的近邻结构进行了分析，分析了在立方钙钛矿BaPbO₃结构中，氧空位的存在是导致BaPbO₃具有类似金属导电性的主要原因。     

金属Cu熔化结晶过程的分子动力学模拟

采用常温、常压分子动力学模拟技术,研究了在周期性边界条件下,由864个Cu原子构成的模型系统的熔化、结晶过程。原子间相互作用势采用EAM势。模拟结果表明：在连续升温过程中,金属Cu在1520 K熔化;以不同的冷速进行冷却,在较慢冷却条件下,液态Cu在1010 K结晶;当冷速较快时,液态Cu形成非晶态。分析了升降温过程中熔体偶分布函数、原子体积、能量、MSD随温度的变化特征。     

贵金属Au冷却过程中结构及能量变化的分子动力学计算机模拟

通过分子动力学方法,研究了不同冷速下贵金属Au在温度2000～300K的冷却过程中微观结构的变化特点。结果发现,冷却速度对Au的微观结构产生重要影响。采用偶关联函数和键对分析技术对原子局域团簇结构进行分析,并考察了冷却过程中原子势能随温度的变化,比较了Au的微观结构转变与能量变化的对应关系,从能量转化的角度对冷却过程中Au的结构变化进行了说明。     

耐蚀合金Au3 Cu高温冷却过程中能量及结构转变的分子动力学模拟

用分子动力学模拟方法对液态Au3Cu冷却过程进行了研究,考察了不同冷却速度下Au3Cu结构变化特点,原子间相互作用势采用F-S多体势,结构分析采用键取向序和对分析技术.计算结果表明,冷却速度对液态Au3Cu能量及结构转变有重要影响,给出了不同冷却速度下液态Au3Cu结构转变的微观信息.     

Cu-Ni合金结构的分子动力学模拟

采用EAM作用势对Cu-Ni合金的结构特性进行了MD模拟研究.通过FZ结构因子可发现,Cu含量的变化对结构因子的波动影响很小,键取向序参数和键对也表现出相似的变化规律,这表明液态Cu-Ni合金对成份变化不敏感,体系中的化学序较弱.将Cu70Ni30合金熔体的FZ结构因子与Waseda的实验结果进行对比,发现二者吻合得较好,表明EAM势可以很好地描绘Cu-Ni合金的结构特性.在快速冷却过程中,除了Cu20Ni80合金外,其他合金成份的双体分布函数的第二峰都发生了劈裂,标志着体系最终形成了非晶结构,而Cu20Ni80合金的双体分布函数却表现出晶体峰的特征.通过对键取向序参数、键型指数以及铜镍原子的有效扩散系数的分析表明,在快速冷却过程中,Cu20Ni80合金最终形成了hcp晶体结构.     

熔体快速冷凝过程的微观结构演化

采用分子动力学模拟技术研究了金属间化合物AuCu3熔体的双体分布函数、键对、多面体、配位数等在快速凝固条件下随温度的变化情况，详细考察了AuCu3中微观组团随温度的演化特点.结果表明，AuCu3熔体降温至700 K时双体分布函数的第二峰已发生劈裂，液态金属中已经产生了非晶态；同时液体中的键对数及多面体数与温度的关系都表明，在上述向非晶转变的过程中，AuCu3熔体的确发生了微观结构组态的变化，其中以液体中的缺陷多面体随温度变化最为剧烈.     

Thermal effect on C-H stretching vibrations of the imidazolium ring in ionic liquids

We have studied temperature dependent IR spectra of the C-H stretching modes of the imidazolium ring in [bmim][PF(6)], [bmim][Tf(2)N], [emim][Tf(2)N], [hmim][Tf(2)N], and [bmim][BF(4)]. Temperatures in this study are from 278 to 348 K at an interval of 10 K. Spectra of the C-H stretching modes have been deconvoluted using our previous computer program of the Voigt-lineshape function. Frequency shifts, Lorentzian spectral widths, and band absorbance were examined as a function of temperature. In order to interpret the observed behaviors, we have developed a simple mechanical model as well as a chemical equilibrium model. The model analyses suggest that enthalpy changes for the cluster and/or ion-pair breaking reactions in the liquid state are several kJ mol(-1) endothermic, and the degree of dissociations of ion pairs or hydrogen bonded clusters is in the range from 0.3 to 0.9 with different magnitudes for the five ionic liquids.     

Nuclear quantum effect and temperature dependency on the hydrogen‐bonded structure of base pairs

The structure of Watson–Crick‐type adenine‐thymine and guanine‐cytosine pairs has been studied by hybrid Monte Carlo (HMC) and path integral hybrid Monte Carlo (PIHMC) simulations with the use of semiempirical PM6‐DH+ method in the gas phase. We elucidated the nuclear quantum effect and temperature dependency on the hydrogen‐bonded moiety of base pairs. It was shown that the contribution of nuclear quantum effect on the hydrogen‐bonded structure is significant not only at low temperature 150 K but also at temperature as high as 450 K. The relative position of hydrogen‐bonded proton between two heavy atoms and the nuclear quantum nature of the proton are also shown. Furthermore, we have applied principal component analysis to HMC and PIHMC simulations to analyze the nuclear quantum effect on intermolecular motions. We found that the ratio of Buckle mode (lowest vibrational mode from normal mode analysis) decreases due to the nuclear quantum effect, whereas that of Propeller mode (second lowest vibrational mode) increases. In addition, nonplanar structures of base pairs were found to become stable due to the nuclear quantum effect from two‐dimensional free energy landscape along Buckle and Propeller modes. © 2013 Wiley Periodicals, Inc.     

Effect of temperature on the mechanism of retention of fullerenes in liquid chromatography using various alkyl bonded stationary phases

Summary The temperature-dependency of the separation of fullerenes in liquid chromatography (LC) has been examined using various alkyl bonded stationary phases. It has been found that a maximum retention temperature exists with long alkyl bonded stationary phases, whereas there is no similar effect with the newly synthesized alkyl bonded phases which have two phenyl groups at the base of the bonded phase. The interpretation of the retention behavior of fullerenes in the low temperature region on alkyl bonded stationary phases is discussed using information obtained by CP-MAS solid-state NMR spectroscopy and LC.     

Melting behaviors of nanocrystalline Ag

In the atomic scale, the melting behaviors of nanocrystalline Ag with mean grain size ranging from 3.03 to 12.12 nm have been investigated with molecular dynamics simulations, and a method to determine the melting temperatures of the infinite polycrystalline nanostructured materials is presented. It is found that the melting in nanostructured polycrystals starts from their grain boundaries, and the relative numbers of the three typical bonded pairs, (1551), (1431), and (1541), existing in the liquid phase, increase rapidly with the evolvement of melting. The melting temperatures of nanocrystalline Ag decrease with decreasing mean grain size, and it can be estimated from the size-dependent melting temperature of the corresponding nanoparticles.     

AuCu3熔体快速冷却过程中的键对与多面体

Based on the FS(Finnis-Sinclair) many-body potential model, the rapid cooling process of a system, which consists of 375 Cu atoms and 125 Au atoms, controlled by period boundary condition was simulated. The dependence of pair distribution function of melten compound AuCu3 on the temperature under these conditions was researched. It can be concluded that the noncrystal exists under 700 K, and the liquid-glass transition temperature is approximately 680 K according to the Abraham′s method. Furthermore, the feature of version of cluster in melten AuCu3 was investigated by Honeycutt pair analysis technique. It is demonstrated that the structural configuration in melten AuCu3 has remarkable variation during the formation of noncrystal according to the relationship between the bonded pairs and polyhedron and temperatures. The defective polyhedra in liquid AuCu3 have greatest changes accompanying the changing temperatures.     

Polymorphism of hydrogen bonding in the short double helixes of oligonucleotides: Semiempirical quantum chemical study

The origin of heterogeneity of nucleotide steps geometry in short double helixes is studied theoretically. By using the semiempirical MNDO/PM3 technique, the stability of “propeller‐like” and “step‐like” forms of base H‐pairing is examined in the structure of oligonucleotide duplexes of different types. The influence of end effects on the process of nucleotides packing, as well as the dependence of duplex curvature on the nature of bonded oligonucleotides, are examined. It is concluded that the structural polymorphism of base pairs most likely determines the unique packing of complementary pairs and their flexibility in DNA structure. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Ni3Al合金液态与非晶中的原子团簇

采用常温常压分子动力学模拟技术，模拟了液态Ni3Al中原子团簇在快速凝固条件下的演变过程，模型采用的是TB(tight binding)作用势.用偶分布函数、键对和多面体等结构参数来描述快速凝固条件下团簇种类和数量的变化，并将团簇结构可视化.在2 000 K下，液态Ni3Al中团簇数量较少，且都是由缺陷二十面体构成；在4×1013 K•s－1的冷速下，团簇的数量随温度的降低不断增加，且出现完整二十面体团簇，体系最终形成了由二十面体和缺陷二十面体团簇网络所组成的非晶结构.