Improving amplitude-modulated signals by re-scaled and twice sampling vibrational resonance methods

Quantum chemical calculations have been employed to study the molecular effects produced by \(\hbox {Cr}_{2}\hbox {O}_{3}/\hbox {SnO}_{2}\) optimised structure. The theoretical parameters of the transparent conducting metal oxides were calculated using DFT / B3LYP / LANL2DZ method. The optimised bond parameters such as bond lengths, bond angles and dihedral angles were calculated using the same theory. The non-linear optical property of the title compound was calculated using first-order hyperpolarisability calculation. The calculated HOMO–LUMO analysis explains the charge transfer interaction between the molecule. In addition, MEP and Mulliken atomic charges were also calculated and analysed.     

农药草甘膦的拉曼光谱计算及分析

草甘膦(glyphosate)是一种高效、低毒、非选择性的芽后除草剂。本文首先给出了草甘膦分子的空间结构图,并用近似方法(Hartree-Fock,HF)对其进行了空间结构优化;然后分别用HF和密度泛函理论(Density Functional Theory,DFT)两种方法基于基组6-31G计算了该分子的振动特性,给出了拉曼光谱和红外光谱强度图,并对比了两种算法的拉曼光谱图和其实验光谱图,结果显示很好的一致性;本文还给出了草甘膦分子的各个键长、键角等空间结构参数,并对草甘膦分子在800cm-1～1600cm-1区间的振动谱做了指认。这些工作将促进针对草甘膦分子的农药残留检测领域的研究。     

Pure rotational spectrum and structural determination of silacyclopentane

The ground state pure rotational spectrum of silacyclopentane (SCP) has been investigated using both Fourier Transform Microwave (FTMW) and chirped pulse Fourier Transform Microwave (cp-FTMW) spectroscopies. In addition to the parent species, the spectra of the ¹³C, ²⁹Si and ³⁰Si singly-substituted isotopologues were recorded in the 6–24 GHz region in natural abundance. Structural analysis confirms that the ground state has C₂ symmetry and the geometric parameters determined based on heavy atom substitution include the bond distances, bond angles and dihedral angles of the SCP ring backbone.     

基于密度泛函理论的三聚氰胺结构及振动光谱研究

利用密度泛函(DFT)算法,对三聚氰胺分子的空间结构进行了优化;然后分别用MP2/6-31G和DFT/DGTIVP两种算法计算了它的拉曼光谱与红外光谱,给出光谱强度图;对比了两种算法的拉曼光谱图和其实验光谱图,结果显示了很好的一致性;给出了三聚氰胺分子中的各原子间键长,键角等空间结构参数;并对三聚氰胺分子在550～3 800cm-1区间的振动谱做了指认。上述工作将有助于食品中三聚氰胺含量测量技术的研究。     

Unusual atomic arrangements in amorphous silicon

The existence of small bond angles (like those of triangles and squares) in amorphous silicon networks were studied by the tight-binding molecular dynamics method, by analyzing the statistical data of Si-Si-Si fragments inside large molecules, and also by the Reverse Monte-Carlo simulation method. The influence of small bond angles on the electronic density of states was revealed.     

The Si,Ge, Sn,Pb doped (6,3) Chiral single-walled carbon nanotubes: A computational study

Electronic structure properties including bond lengths, bond angles, dipole moments (μ), energies, band gaps, NMR parameters of the isotropic and anisotropic chemical shielding parameters for the sites of various atoms were calculated using the density functional theory for Si, Ge, Sn, Pb doped (6,3) Chiral single-walled carbon nanotubes (SWCNTs). The calculations indicated that average bond lengths were as: Pb3C>Sn3C>Ge3C>Si3C>C3C. The dipole moments for Si, Ge, Sn, Pb doped (6,3) Chiral single-walled carbon nanotubes structures show fairly large changes with respect to the pristine model.     

Computational Studies on the Ground State Tautomer,Hydrogen Conformations and Vibrational Spectroscopic Analysis of Antitumor Agents:3-Deazauracil and 6-Azauracil

The ground state hydrogen conformations and vibrational analysis of 3-deazauracil (3DAU) and 6-azauracil (6AU) tautomers (4-enol and 2,4-diol forms) have been calculated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-311++G(d,p) basis set level. The calculations have shown that the most probably preferential tautomer of 3DAU and 6AU are the 4-enol form, which gives best fit to the corresponding experimental data. The ground state conformer of the 2,4-diol form has two O-H bonds which are oriented externally and internally (to the N-H bond). The vibrational analyses of the ground state conformer of each tautomeric form of 3DAU and 6AU were done and their optimized geometry parameters (bond lengths and bond angles) were given. Furthermore, from the correlations values it was concluded that the B3LYP method is superior to the HF method for both the vibrational frequencies and the geometric parameters.     

Effect of bond angle and dihedral angle disorder on diamagnetic susceptibility of tetrahedrally coordinated amorphous semiconductors

We study the effect of bond angle and dihedral angle disorder on the diamagnetic susceptibility (χ) of a model amorphous semiconductor by adopting a linear combination of hybrids formalism. We have constructed orthormal basis states for the disorder network by introducing distortion in bond angles and dihedral angles. We have used the disorder basis states in the expression for χ and adopted suitable averaging techniques to obtain χ in terms of disorder parameters, which shows interesting results.      

异硫氰基-孔雀石绿的拉曼光谱计算及分析

异硫氰基-孔雀石绿(malachite green isothiocyanate,MGITC)是应用于细胞探测,生物组织成分分析和细胞成像等方面的拉曼探针分子.本文首先给出了MGITC分子的结构图,并用密度泛函(DFT)算法对其进行了空间结构优化;然后分别用Hartree-Foek(HF)和MP2两种算法基于STO-3G基组计算了它的拉曼光谱与红外光谱,给出光谱强度图;并对比了两种算法的拉曼光谱图和其实验光谱图,结果显示了很好的一致性;本文还给了MGITC分子中的各个原子键长,键角等空间结构参数;并对MGITC分子在550～4 200cm-1区间的振动谱做了指认.这些工作将促进MGITC作为探针分子在生物学领域的应用.     

Conformational studies of poly(methacrylic acid). I. Conformational energy calculations on lsotactic and syndiotactic poly(methacrylic acid)

The conformational energies of isotactic and syndiotactic poly (methacrytic acid) were calculated for isolated chains in order to determine the most probable helical conformations. It was concluded that the most probable backbone conformation of the isotactic polymer is either a 5₂ or 8₃ helix, where the internal rotations of the two helices are nearly equal. The left-handed and right-handed conformations were also essentially equienergy conformations. Two lowenergy helical conformations were found for the syndiotactic polymer. One of these conformations had backbone internal rotations nearly identical to those of the 5₂ and 8₃ helices of isotactic poly(methacry1ic acid). The second conformation was a nearly planar structure containing two monomer units in the axial repeat unit, with backbone rotation angles nearly identical to those of the 5₂ and 8₃ helices or their negatives.

Deformation of the backbone C─C─C bond angles was considered in the conformational energy calculations. The optimum bond angles for both isotactic and syndiotactic polymer chains were considerably larger than the normal tetrahedral bond angle. The relative energies calculated for helical conformations were influenced by the backbone bond angles. It was demonstrated that the failure to consider backbone bond-angle deformation may lead to erroneous conformational assignments in disubstituted vinyl polymers.     

丝网印刷FeS2（pyrite）薄膜的结构及光电性能

采用丝网印刷方法制备了FeS₂(pyrite)薄膜，用x射线衍射确定了样品FeS₂(pyrite)薄 膜的 晶体结构，并用Rietveld方法对样品的结构进行了精修，确定了样品的点阵常数、键长、键 角、硫原子占位等结构参数.研究了膜厚对方块电阻、载流子浓度、霍尔迁移率、光能隙等 光电参数的影响. 关键词： 丝网印刷 薄膜 结构 Rietveld方法 光电性能     

An icosahedral quasicrystalline model for amorphous semiconductors

In the first article of this series an icosahedral quasicrystal with a tetracoordinated decoration of atoms was introduced as a model for amorphous semiconductors. The electronic structure is one of its most interesting features. Based upon a LCAO tight binding scheme with five orbitals sp³s* per atom the electronic density of states (DOS) is calculated by use of the recursion method. Various effects of the specific geometry on the DOS are investigated, including the topology of the tetracoordinated network, the corresponding dihedral angles, bond angles, bond lengths, and dangling bonds. These geometrical parameters are treated separately and therefore reveal their distinct influences on the DOS. The resulting effects are discussed regarding the DOS as a whole, while details are provided about variations of the outer band edges, shifts of maxima and first moments of uppermost valence band and lowest conduction band, and — most important — changes in the central gap. The properties of single wave functions are subject of the third article in this series.     

电子被等电子分子的散射总截面的研究

讨论等电子分子的分子 (电子数Ne=10 :HF ,H2 O ,NH3,CH4 ;Ne=14:N2 ,CO ,HCN ,C2 H2 ;Ne=18:HCl,CH3F ,H2 S ,SiH4 ,C2 H6)被电子散射的总截面与其键长、键角之间的关系 ,得到了利用键长、键角计算电子被分子散射总截面经验公式 ,并与已有的拟和公式、经验公式的计算结果进行了比较     

塑化剂邻苯二甲酸二辛酯的拉曼光谱计算及分析

近几年,国内有关塑化剂的食品安全事件频发,迫切需求加强对于食品中塑化剂的检测研究工作。邻苯二甲酸二辛酯是塑化剂的一种。理论计算和实验测量了邻苯二甲酸二辛酯的拉曼光谱。利用密度泛函理论DFT(B3LYP)的三参数混合方法对其进行了空间结构优化;然后分别用(Hartree-Fock)HF/3-21G和DFT/3-21G两种算法计算了它的拉曼光谱和红外光谱,给出了光谱强度图。实验测量了分析纯级邻苯二甲酸二辛酯的拉曼光谱,并和理论计算结果进行了对比,显示了很好的一致性,与此同时由于计算方法的不同,从图中可以看出Gaussian计算的HF和DFT算法无论是峰的位置还是相对强度等都均存在差别。还给出了常用塑化剂邻苯二甲酸二辛酯的各个键长、键角等空间结构参数,并对邻苯二甲酸二辛酯分子在400～3 500 cm-1区间的振动谱做了指认。报道了常用塑化剂邻苯二甲酸二辛酯的拉曼光谱研究工作。这些工作将有助于拉曼光谱技术在食品检测领域的研究和应用。     

A study of the structural and spectral characteristics of free and bound water in kaolinite

The dependence of the Si–O stretching vibration line intensity in the IR spectrum of kaolinite on the humidity of this mineral has been experimentally investigated. The experimental data were interpreted on the basis of density functional theory (DFT) calculations with allowance for the real crystallographic features of the kaolinite sample, determined by structural analysis. Some specific features of the intensity behavior in the plastic state are revealed, which can be used to develop techniques for determining its limits. The differences in the O–H bond lengths and H–O–H angles for the H₂O molecules adsorbed by basal surfaces and located in the porous space of the mineral are determined. Based on the DFT data, it was found that bond lengths and bond angles for a water molecule adsorbed on the siloxane surface are systematically smaller than for a water molecule adsorbed on the hydroxyl surface.     

水玻璃化过程的氢键结构特性

为了解玻璃化过程氢键结构特性,采用分子模拟的手段计算了三种压力下的水玻璃化过程氢键的角度、距离、生命期和数量.计算结果显示:(i)氢键角度呈现泊松分布的特征,随着温度降低分布氢键角度分布范围变窄,峰值变高,在0～13°范围,随温度降低,分布数值变大;而在大于13°,随温度降低,分布数值变小;(ii)氢键距离也呈现泊松分...     

Are LCAO-MO Models Useful Estimators for Electric Field Gradients in Simple Molecules?

In this tutorial paper we compare the ab-initio calculations of electronic charge densities and related electric field gradients in simple molecules like H₂ as well as the triangular H₃ with variable bond distance and bond angle using the Amsterdam Density Functional (ADF) code with calculations based on a simple linear combination of hydrogen 1s-orbitals. In order to gain more insight into ADF – or other ab-initio – calculations it is rather useful to vary structural parameters. In addition to geometry optimisations we propose to vary bond distances and bond angles over extended ranges in order to arrive at a better interpretation of the results.     

用一维和二维核磁共振波谱研究吗啡和可待因的分子构型

用360MHz超导核磁共振波谱仪测定了吗啡(morphine)和可待因(codeine)的质子耦合常数。用二维J-谱验证了一维质子谱的J-耦合。用一系列改性的Karplus公式计算了二面角(dihedral sngles),估算了吗啡和可待因的分子构型(configuration)。     

Determination of the moment of inertia of methyl groups: Analysis of the millimeterwave spectra of cis-propanal and methylthioethyne

The ground state rotational spectra of methylthioethyne and cis-propanal have been investigated. An overall fit of the measurements using the Internal Axis Method has allowed us to accurately determine the internal rotation parameters. The moments of inertia of methyl groups obtained from an internal rotation analysis are reviewed. They are compared to the values calculated using two empirical correlations found by McKean: between the isolated stretching frequencies and the corresponding CH bond lengths or the HCH angles.