Ne-CH4分子间相互作用势的局域密度近似计算

利用基于密度泛函理论框架下的局域密度近似方法对Ne-CH4分子间的相互作用势进行了计算. 发现: 当Ne原子和CH4分子之间的距离约为5.8 a.u.时, 计算的势能曲线存在最小值, 对应的势阱深度约为0.053 eV. 计算结果与实验值符合较好.     

水二聚体分子间相互作用势

利用超分子二阶到四阶多体微扰理论和扩展的相关一致基组(aug-cc-pVTZ)结合有效的中点键函数(3s3p2d1f1g)计算水二聚物的平衡结构和分子间相互作用势,并用平衡方法修正基组重叠误差.在MP2/aug-cc-pVTZ理论级别优化水二聚物几何构型.与正常优化的结果相比,平衡修正优化得到的RO-O和α值分别轻微的增加0.002 nm和0.19°,同时,θ值减小0.013°.在MP2水平利用扩展的相关一致基组结合有效键函数,预言了RO-O和ΔECP值分别为0.0923 nm和-4.86 kcal/mol,计算结果与实验值符合得很好.用exp-4.2势函数拟合分子间相互作用能的离散点,拟合结果与从头算计算的结果一致.     

低密度氢气的分子间平均相互作用势理论和计算

本文提出了分子单中心模型,并通过对构型的平均,两个定理的提出与证明,色散能修正的证明,从数学上论证了这个模型的合理性。由此模型可以直接求出两个氢分子间的平均相互作用势,从而改变了长期以来,总是先算有限几种构型然后再作平均的传统作法。通过数字计算,得到了迄今为止最好的全程平均相互作用势曲线。势阱深度及平衡分子间距分别为-2.91meV和3.44(实验值:-2.85～-3.00meV,3.43～3.49)。     

局域密度近似理论的适用范围及其理论证明

在电子密度中,可以假定存在一种能产生交换相关能的非局域空穴。通过该假定可将存在于局域密度理论中的电子自相互作用消除。由这种交换相关能所导出的非局域电子密度势具有两方面的作用:一方面会影响到由空穴产生的静电势;另一方面当空穴的大小和形状随其密度变化而引起能量变化时,它也会影响到描述这些变化的项。迄今为止,所有以往曾研究过此问题的国外学者都只考虑了前一方面的影响而忽略后一方面的作用。本文对包含这些项所引起的各种效应进行了全面而严格的检验,并采用了局域近似或完全忽略;若完全忽略会产生各种各样的无序波函数。本文证明对这些项可进行一般的局域估价,这种方法较之于精确处理要简便得多。 关键词：     

TATB分子的结构及分子间相互作用

采用Hartree-Fock方法和密度泛函BPW91方法,对TATB双分子系统的几何结构和能量进行了优化和计算,得到双分子共平面的平衡结构.结果表明在TATB分子内部H和O之间存在着明显的氢键.分子之间的相互作用使TATB分子的对称性下降.一般地,没有充分计入分子之间的相互作用的影响时,计算得到的C-N键长比实验测得值大,而计算得到的C-C键长比实验测得值小.计算并讨论了TATB分子之间的相互作用能,表明TATB分子形成晶体结构时,应当以层状晶体结构最为稳定.     

LLM-105的分子间相互作用和热力学性质

应用第一性原理可以计算含能材料0 K下的结构和物理性质,但温度效应的缺失通常会导致计算数据与实验结果产生偏差.同时,与温度相关的热力学参数是含能材料在宏观和介观尺度下建模的关键输入.为此,本文以高能低感炸药1-氧-2, 6-二氨基-3, 5-二硝基吡嗪(LLM-105)为研究体系,基于准简谐近似,采用色散修正的密度泛函理论研究温度加载下LLM-105的分子间相互作用和热力学性质.晶格参数和热膨胀系数的演化表明LLM-105分子间相互作用具有强烈的各向异性,其中b轴方向(分子层间)的膨胀率远高于ac平面(分子层内). Hirshfeld表面及其指纹图分析进一步证实LLM-105的分子间相互作用主要取决于O···H构成的氢键.结合Mulliken布居数和结构分析,温度加载下氢键相互作用的变化可诱发硝基旋转,并使得C—NO₂键的强度明显减弱,为高温分解反应的触发键提供了理论依据.此外,本文计算了等容和等压条件下的热容、熵以及等温和绝热条件下的体模量等基础热力学参数.其中绝热条件下的体模量与实验值吻合,同时体模量随温度的演化反映了LLM-105在温度加载下的软化行为.上述...     

C60分子之间相互作用势的Kihara形式

根据Ｃ６０－晶体的升华焓，晶包参数和压缩系数，求得了Ｃ６０分子之间相互作用势的Ｋｉｈａｒａ形式，并且讨论了简单的Ｌｅｎｎａｒｄ－Ｊｏｎｅｓ势不能很好地描述Ｃ６０分子之间的相互作用。根据Ｃ６０分子之间相互作用势的Ｋｉｈａｒａ形式，计算了不同Ｃ６０晶型的某些性质，讨论了Ｃ６０晶体不同晶型的稳定性问题。     

锂原子与部分惰性气体原子间相互作用势的计算

基于碱金属原子与惰性气体原子间相互作用的交换势主要来自碱金属原子的最外层S电子与惰性气体原子的最外层S电子之间 ,将面积分方法 (thesurfaceintegralmethod)推广 ,计算了Li原子与Ne、Ar、Kr和Xe原子间相互作用的vanderWaals势能曲线。其势阱的位置和深度与实验结果和其它理论计算结果符合得相当好     

弱相互作用费米气体的热力学性质

根据赝势法导出无外势时弱相互作用费米气体的化学势、内能和定容热容的解析表达式.在此基础上，采用局域密度近似研究谐振势中弱相互作用费米气体的热力学性质，探讨粒子间相互作用对系统性质的影响. 关键词： 费米气体 相互作用 赝势法 局域密度近似 热力学性质     

Doping-induced spin-manipulation in complex trimer system Ca3Cu3(PO4)4: A density functional investigation

Doping induced spin-manipulation with magnetic (Ni) and non-magnetic (Mg) dopants constitutes the experimental attempts to obtain a singlet ground state system from the linear chain Heisenberg antiferromagnetic Cu-based d⁹ spin-1/2 trimer compound Ca³Cu³(PO⁴)⁴ with doublet ground state. The present study is a density-functional investigation of the effects of such doping on the spin-exchange mechanism and electronic structure of the parent compound. Site-selective doping with zero-spin dopants like Mg is proved to be more efficient than an integral spin dopant Ni in obtaining a spin-gap system with singlet ground state, as also observed in the experimental studies. Doping induced dimerized state is found to be the lowest in ground-state energy. Calculated spin exchange couplings along various possible pathways are observed to attain good agreement with earlier experimental results with suitable optimization of Coulomb repulsion (U) and exchange (J) parameters.     

Rydberg transition frequencies from the local density approximation

A method is given that extracts accurate Rydberg excitations from density functional calculations in the local density approximation, despite the short-ranged potential. For the case of He and Ne, the asymptotic quantum defects predicted by the calculations are in less than 5% error, yielding transition frequency errors of less than 0.1 eV.     

Intermolecular interaction in plant oils from refractive and density measurements

Refractive indices n and density ρ of three plant oils (Anise, Nigelle, and Juniper berries) have been measured in the temperature range of 10–60°C. The model of the effective electric field E′ acting on a molecule in the material, E′ = E + x4πP, with the unlimited value of the coefficient of polarization input x has been applied to the analysis of the results obtained. The value x of the oils studied have been found to be in the range of 0.193–0.269, which is smaller than a similar value for water (x _water > 0.3), known as a strong polar liquid.     

Hyperfine interaction of Eu in Eu2TiO4

The hyperfine interaction of ¹⁵¹Eu in Eu₂TiO₄ has been measured using the Mössbauer Effect. Using the four-fold symmetry of the Eu²⁺ site, it has been found that the nuclear quadrupole moment ratio of the first-excited to the ground states of ¹⁵¹Eu is R = 1.34 ±0.03, and the quadrupole interaction energy is ρ²qQ_o = -(190 ± 7) MHZ. Below T_c = 7.8K, the magnetic hyperfine field H_hf points close to the direction of the four-fold axis. The zero-degree value of H_hf is estimated to be (305 ± 3) kOe.     

Ordered local distortions in cubic FeCr2S4

Mössbauer spectra of ⁵⁷Fe in FeCr₂S₄ and Co_0.02Cr₂S₄ were taken at various temperatures. The temperature dependence of H_h? and eQV_zz in Co_0.98Fe_0.02Cr₂S₄ can be explained as the combined effect of exchange, spin-spin, and spin-orbit interaction. In FeCr₂S₄ at low temperatures H_h? is not reduced and the EFG is no longer axially symmetric. This behaviour is explained on the basis of a magnetically induced quadrupole splitting influenced by negatively coupled local distortions ordered in an antiparallel way in two sublattices, which coincide with the two Bravais lattices of tetrahedral sites in the spinel lattice. The ‘antiferrodistortive’ transition occurs between 13 and 23 K.     

Separable energy-dependent approximation to local potentials

An extension of the single-pole separable approximation of a two-body t-matrix in which the effects of several poles are included is made. The simple form for the t-matrix derived from a single separable potential is retained. However, the separable potential is constructed using an energy-dependent superposition of the states corresponding to the various poles. The energy dependence is chosen so as to obtain the correct residue of both the on-shell and off-shell t-matrices at each of these poles, while preserving unitarity. The formalism is specialized to the case of s-wave scattering from an attractive square well. Comparison to the exact s-wave cross section gives good results.     

Desorption of dimethylformamide from Zn4O(C8H4O4)3 framework

Both dimethylformamide (DMF) and diethylformamide (DEF) are important solvents for the synthesis of Zn₄O(C₈H₄O₄)₃ framework (MOF-5). It is generally recognized that DMF molecules can be completely displaced by CH₂Cl₂ during the synthesis of MOF-5. Herein, however, it was found that the DMF molecules inside the pores of the MOF-5 framework cannot be displaced by CH₂Cl₂. The desorption of the DMF molecules from the pores, which requires a temperature of 100 °C or above, is the first order with activation energy of 56.38 kJ/mol. In contrast, DEF molecules can be completely displaced by CH₂Cl₂ during the synthesis of MOF-5, because DEF molecules cannot penetrate into the pores of the MOF-5 paste.     

Ion diffusion in the high-temperature phases Li2SO4, LiNaSO4, LiAgSO4 and Li4Zn(SO4)3

Diffusion in the four high-temperature sulphate phases Li₂SO₄, LiNaSO₄, LiAgSO₄ and Li₄Zn(SO₄)₃ was studied extensively some 20–30 years ago. We have now carried out a re-evaluation where we include information obtained from a number of studies of other properties. The data are adjusted slightly due to the use of another type of regression analysis. It is characteristic of the four phases that they are both plastic crystals and solid electrolytes (superionic conductors). The cause of the high conductivity is that the mobility of the cations is strongly enhanced by the rotational motion of the translationally static sulphate ions. This is observed not only for the abundant cations, but also for other cations present (mono- as well as polyvalent) and for monovalent anions. Furthermore, both bulk diffusion and transfer along high diffusivity paths are affected. In addition, one can distinguish between different contributions to the bulk diffusion. The ionic radius is a very important parameter, since it determines the solid solubility and the distribution of the ions between the sites that are available in the lattice. All this affects the relative importance of several competing diffusion mechanisms. This gives a qualitative explanation of an anomalous correlation which has been observed in FCC Li₂SO₄ for monovalent ions (cations as well as anions), namely that both the diffusion coefficients D, and the activation energies Q, decrease when the radius is increased. This holds for hard-core cations (Li, Na, K, Rb), polarizable cations (Ag, Tl) and anions (F, Cl, Br). On the other hand, the situation is normal for divalent cations for which an increase in D corresponds to a decrease in Q. This is the case for hard-core ions (Mg, Ca) as well as for polarizable ones (Zn, Cd, Pb). Migration of the large ions Cs⁺ and SO²⁻₄ appears to be specially sensitive to how the experiment is prepared. Diffusion in BCC LiNaSO₄ and LiAgSO₄ has been studied for the two main cations as well as for some dopant ions. A general conclusion is that studies of diffusion of several ions in the same structure can give information that cannot be obtained by other types of experiments.