共查询到18条相似文献,搜索用时 78 毫秒
1.
采用量子化学自洽场方法及原子团簇理论对固氦晶格原子势能进行多体展开,定量确定了最近邻原子间距R在0.26—0.175nm之间,短程的两体到五体相互作用对晶体结合能及压缩特性的贡献,并对不同间距下多体展开式的截断位置进行了讨论. 结果表明:当最近邻原子间距R在0.26—0.175 nm之间取值,在具有hcp相结构的晶格中,氦原子势能的多体展开式是一收敛的交错型级数,该级数中两体项、四体项为正值,而三体项、五体项为负值. 当R在0.26—0.23 nm之间取值时, 仅保留级数中两体和三体项就能很好地描述晶格原子势能;当R在0.23—0.20 nm之间取值,多体展式需要展开到四体相互作用项;当R在0.20—0.175 nm之间取值必须再加入五体项贡献. 考虑到五体相互作用后,理论计算已能圆满地解释目前固氦等温压缩数据,其最大压力达 60GPa.
关键词:
固氦
状态方程
多体相互作用 相似文献
2.
X射线衍射实验显示固氩是面心立方(fcc)晶格结构,目前对晶体氩的研究只限于两体,三体以及四体相互作用势.本文利用多体展开方法和超分子单、双(三)重激发耦合簇理论(CCSD(T))对固氩fcc晶格结构的三体和四体的几何构型、几何参数、不同体积下所有三体和四体构型的势能以及各构型所占比例等几个方面进行了准确的量子化学计算.结果表明:所有三体构型中对总的三体势能贡献最大的是构型1、构型6、构型12和构型23;三体势及其交换部分和色散部分的计算结果与现有解析经验势在长程部分符合得非常好,但在短程部分有较小差异.所有的四体构形中对总的四体势能贡献最大的是构型1,构型2,构型4,构型5,构型7和构型8;四体势及其交换势部分和色散部分的计算结果尚无解析经验势可比较.利用这些特殊构型的相关数据并结合其它构型,可拟合出更准确的三体经验势函数及其参数,也为拟合四体经验势函数及其参数提供了重要的参考价值. 相似文献
3.
郑兴荣 《原子与分子物理学报》2016,33(6)
X射线衍射实验显示固氩是面心立方(fcc)晶格结构,目前对晶体氩的研究只限于两体,三体以及四体相互作用势。本文利用多体展开方法和超分子单、双 (三)重激发耦合簇理论(CCSD(T))对固氩fcc晶格结构的三体和四体的几何构型、几何参数、不同体积下所有三体和四体构型的势能以及各构型所占比例等几个方面进行了准确的量子化学计算。结果表明:所有三体构型中对总的三体势能贡献最大的是构型1、构型6、构型12和构型23;对三体势及其交换部分和色散部分的计算结果与现有解析经验势在长程部分符合得非常好,但在短程部分有较小差异。所有的四体构形中对总的四体势能贡献最大的是构型1,构型2,构型4,构型5,构型7和构型8;对四体势及其交换势部分和色散部分的计算结果尚无解析经验势可比较。利用这些特殊构型的相关数据并结合其它构型,可拟合出更准确的三体经验势函数及其参数,也为拟合四体经验势函数及其参数提供了重要的参考价值。 相似文献
4.
5.
6.
用量子力学修正的WCA液体变分微扰理论计算了液氦冲击压缩曲线,计算中体系分子间相互作用势选择EXP-6有效两体势模型,两体势参数通过对实验数据的拟和优选。计算结果在一次冲击压力范围内,冲击温度及压力与Nellis等人的实验数据符合很好,二次冲击数据与实验值稍有偏差,但也在其误差范围内,由于二次冲击只有一个实验点,因此实验数据不能提供更多的信息以供比较。计算结果表明与其他分子间相互作用势相比,选择α值为12.7的EXP-6势更为准确地反映了液氦分子间的相互作用。 相似文献
7.
8.
采用Lowdin方法计算了处于压缩状态的氦原子团簇He9体心立方向型的排斥势及其多体分量,并由此计算出团簇微观压强及其多体分压强。结果发现,多体作用对氦原子团簇He9压缩特性贡献较大。在相同体积下,由两体近似方法计算的体系压强比多原子体系实际压强偏高10%~30%;考虑三体分压强修正后,近似理论的计算值又会偏低1.5%~10%;只有同时考虑三体、四体修正后,近似理论计算值与实际多原子体系的压强值基本一致。团簇He9所表现出的压缩特性与固态氦的实验结果相符合。 相似文献
9.
10.
11.
O. P. Nikolaeva 《Russian Physics Journal》2008,51(11):1174-1177
A relationship between correlations and anharmonic effects in solid helium is investigated based on the Bogolyubov method.
To this end, the internal energy of the system and the expression for the pressure derived with the use of one- and two-particle
density matrices are considered for which the series of perturbation theory converge at any arbitrary temperature. The results
obtained are compared with the available experimental data on diffraction of synchrotron radiation by helium crystals.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 54–56, November, 2008. 相似文献
12.
Cai Lingcang Chen Qifeng Gu Yunjun Zhang Ying Zhou Xianming Jing Fuqian 《中国科学G辑(英文版)》2005,48(2):695-705
Hugoniot curves and shock temperatures of gas helium with initial temperature 293 K and three initial pressures 0.6, 1.2,
and 5.0 MPa were measured up to 15000 K using a two-stage light-gas gun and transient radiation pyrometer. It was found that
the calculated Hugoniot EOS of gas helium at the same initial pressure using Saha equation with Debye-Hückel correction was
in good agreement with the experimental data. The curve of the calculated shock wave velocity with the particle velocity of
gas helium which is shocked from the initial pressure 5 MPa and temperature 293 K, i.e., theD ≈u relation,D=C
0+λu (u<10 km/s, λ=1.32) in a low pressure region, is approximately parallel with the fittedD ≈u (λ=1.36) of liquid helium from the experimental data of Nellis et al. Our calculations show that the Hugoniot parameter λ
is independent of the initial density p{in0}. TheD≈u curves of gas helium will transfer to another one and approach a limiting value of compression when their temperature elevates
to about 18000 K and the ionization degree of the shocked gas helium reaches 10−3. 相似文献
13.
CAI Lingcang CHEN Qifeng GU Yunjun ZHANG Ying ZHOU Xianming & JING Fuqian Laboratory for Shock Wave Detonation Physics Research Institute of Fluid Physics Mianyang China 《中国科学G辑(英文版)》2005,48(6):695-705
Helium, hydrogen, and their isotopes are the simplest monoatomic and diatomic molecules. It is relatively easy to describe their properties using the basic principles of quantum mechanics. In condensed matter physics, hydrogen and helium serve as the models for the condensed matter properties at extreme conditions so that both experi- mental and theoretical physicists pay much attention to the study of their properties[1], especially the insulator-metal transition of hydrogen[2]. The aim to st… 相似文献
14.
Although rare-earth metals have increasingly received attention for use in the storage and transportation of the tritium used in nuclear fusion reactions, they still face great challenges, such as the effect of helium on the mechanical properties of different erbium hydrides. In this work, first principles are used to study the mechanical properties(elastic constants, Young's modulus, transverse shear modulus and bulk modulus) of different erbium hydrides exposed to helium. The Young's modulus, the transverse shear modulus and the bulk modulus are given based on the elastic constants calculated according to first principles. It is found that the mechanical properties of all three erbium hydrides decrease in the presence of helium, and the decline of the mechanical properties of ErH_3 is the most serious. To explain the reason for the decrease in the mechanical properties, the densities of the states of erbium hydrides are calculated. During the calculations, helium embrittlement is not found and the ductility of the erbium hydrides improves following the production of helium at the helium concentrations considered in this work. 相似文献
15.
借助不可约张量理论,导出了氦原子2^3P态自旋-其他轨道相互作用能的理论计算式,在推导过程中完成了所有角向积分和自旋求和计算. 相似文献
16.
Solid helium bubbles were directly observed in the helium ion implanted tungsten(W), by different transmission electron microscopy(TEM) techniques at room temperature. The diameters of these solid helium bubbles range from1 nm to 8 nm in diameter with the mean bubble size about 3 nm. The selected area electron diffraction(SAED) and fast Fourier transform(FFT) images revealed that solid helium bubbles possess body-centered cubic(bcc) structure with a lattice constant of 0.447 nm. High-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)images further confirmed the existence of helium bubble in tungsten. The present findings provide an atomic level view of the microstructure evolution of helium in the materials, and revealed the existence of solid helium bubbles in materials. 相似文献
17.
YU Kai-Zhi 《理论物理通讯》2007,48(5):913-916
Relativistic many-body perturbation calculation is applied to calculate the hyperfine constants for the lowlying states 6S1/2, 6P1/2, 6P3/2, 5D3/2, and 5D5/2 in the alkaline earth ion ^137Ba^+. The zeroth-order hyperfine constants are calculated with Dirac-Fock wave functions, and the finite basis sets of the Dirac-Fock equation are constructed by B splines. With the finite basis sets, the core polarization and the correlation effect are calculated. The final results for magnetic dipole hyperfine a constants are obtained. 相似文献
18.
采用包含两个斯莱特基的"双ζ"函数说明了利用自洽场法求解基态氦原子Roothaan-Hartree-Fock方程的数值过程,计算得基态能量为-2.862 568 Hartree.利用基态的对称性,提出了通过求解泊松方程来计算库仑算符的方法,给出了交叠矩阵和单电子算符的矩阵元,并对自洽的标准作了讨论. 相似文献