基态原子与理想金属Au表面间的范德瓦尔斯作用

研究了基态碱金属原子与理想金属Au表面间的范德瓦尔斯(vdW)作用.通过分析电四极跃迁对vdW的贡献,构建了计算超精细能级碱金属原子与理想金属表面间vdW作用系数C3的理论模型.以85Rb、133Cs为例,计算了其基态原子超精细能级的C3系数.其中85Rb: 52S1/2 (F=2)及52S1/2 (F=3)对应的C3系数分别为:2.2409 及2.2425 ;133Cs: 62S1/2 (F=3)及62S1/2 (F=4)分别对应 2.4480 及2.4538 .研究还发现随着 的增大,C3增大,z (原子与金属表面之间的距离)不变时,原子与理想金属表面间vdW作用增强. 这一研究在实现原子囚禁及介质表面量子反射等方面具有重要意义     

基态原子与理想金属Au表面间的范德瓦尔斯作用及超精细能级C_3的估算

研究了基态碱金属原子与理想金属Au表面间的范德瓦尔斯(vdW)作用.通过分析电四极跃迁对vdW的贡献,构建了计算碱金属原子的超精细能级与理想金属表面间vdW作用系数C3的理论模型.以85 Rb、133Cs为例,计算了其基态原子超精细能级的C3系数.其中85 Rb:52S1/2(F=2)及52S1/2(F=3)对应的C3系数分别为:2.2409 KHzμm3及2.2425 KHzμm3;133 Cs:62S1/2(F=3)及62S1/2(F=4)分别对应2.4480KHzμm3及2.4538KHzμm3.研究还发现随着F的增大,C3增大,z(原子与金属表面之间的距离)不变时,原子与理想金属表面间vdW作用增强.这一研究在实现原子囚禁及介质表面量子反射等方面有一定的意义.     

超精细能级中133CS激发态(｜62D3/2F>)原子与理想金属表面间范德瓦尔斯作用系数C3的估算

利用碱金属原子与理想金属表面间范德瓦尔斯(vdW)作用势和不可约张量方法,首次计算了133CS激发态62D3/2 (F=2,3,4,5)原子超精细结构的C3系数.数值分别对应为:17.9956 、18.0796 、18.0857 及18.1756 .为了说明其结果的准确性,还与其他作者的理论数据和相关实验数据进行了比较,结果表明本文所得到的133CS激发态62D3/2 (F=2,3,4,5)原子的C3数值是可靠的.     

超精细能级中85Rb激发态(｜52P1/2F>、｜52P3/2F>)原子与理想金属表面间范德瓦尔斯作用系数C3的估算

利用碱金属原子与理想金属表面间范德瓦尔斯(vdW)作用势和不可约张量方法,首次计算了85Rb激发态52P1/2 (F=2,3)及52P3/2 (F=1,2,3,4) 原子超精细结构的C3系数.数值分别对应为:4.0542 、4.0553 及4.3012 、4.3312 、4.3369 、4.3104 .为了说明其结果的准确性,还与其他作者的理论数据和相关实验数据进行了比较,结果表明本文所得到的85Rb激发态52P1/2 (F=2,3)及52P3/2(F=1,2,3,4)原子的C3数值是可靠的     

超精细能级中~(133)C_S激发态(|6~2D_(3/2)F>)原子与理想金属表面间范德瓦尔斯作用系数C_3的估算

利用碱金属原子与理想金属表面间范德瓦尔斯(vd W)作用势和不可约张量方法,导出超精细能级中碱金属原子特定量子态C3的解析表达式,完成133CS原子62D3/2(F=2,3,4,5)的C3数值计算,计算结果表明随着的增大,C3增大,z(原子与金属表面之间的距离)不变时,铯原子与理想金属表面间vd W作用增强.同时对于由电四极矩作用产生的C31效果因贡献不显著,C3数值结果并未见到有异常波动现象.     

超精细能级中85Rb激发态(｜52P1/2F>、｜52P3/2F>)原子与理想金属表面间范德瓦尔斯作用系数C3的估算

利用碱金属原子与理想金属表面间范德瓦尔斯(vdW)作用势和不可约张量方法,首次计算了85Rb激发态52P1/2 (F=2,3)及52P3/2 (F=1,2,3,4) 原子超精细结构的C3系数.数值分别对应为:4.0542 、4.0553 及4.3012 、4.3312 、4.3369 、4.3104 .为了说明其结果的准确性,还与其他作者的理论数据和相关实验数据进行了比较,结果表明本文所得到的85Rb激发态52P1/2 (F=2,3)及52P3/2(F=1,2,3,4)原子的C3数值是可靠的     

超精细能级中~(133)Cs激发态|6~2P_(3/2)F〉(F=2,3,4,5)原子与理想金属表面间范德瓦尔斯作用系数C_3的估算

利用碱金属原子与理想金属表面间范德瓦尔斯(vd W)作用势和不可约张量方法,计算~(133)Cs激发态|6~2P_(3/2)F〉(F=2,3,4,5)原子超精细结构的C_3系数.数值分别为:4.338 5 k Hz·μm~3、4.361 9 k Hz·μm~3、4.368 0及4.346 7 k Hz·μm~3.与其它理论数据和实验数据比较,结果表明本文所得到的~(133)Cs激发态|6~2P_(3/2)F〉(F=2,3,4,5)原子的C_3数值是可靠的.     

基态超精细能级光泵浦效应对原子光致漂移速率影响研究

在光致漂移现象中,基态超精细能级光泵浦效应会影响激光作用下原子在各个能级的布居情况,进而影响原子光致漂移速率的大小.基态超精细能级光泵浦效应影响机制的研究有助于漂移速率和同位素分离选择性的优化.基于原子光致漂移速率方程,利用强碰撞模型描述原子与缓冲气体的碰撞作用,运用数值方法对速率方程进行求解计算,研究了基态超精细能级...     

四参数法计算氦原子基态能级研究

在求解氦原子径向Schr dinger方程时,设计了含有四参数的基态波函数,推导出含有四参数的氦原子基态能级表达式,分别采用Matlab 7.0最优化运算和Monte-Carlo法,计算了氦原子的基态能量,得到了相应的波函数.将计算结果与其它文献采用变分法所得计算值及实验值进行了比较,结果表明:这种方法不仅计算简便有效,准确性较高,而且所得氦原子基态空间波函数自动满足空间对称性的要求.     

用并行计算的方法研究He原子基态关联能

用组态相互作用方法计算了Ｈｅ原子基态电子关联能，为了既得到较高精度又克服计算机上遇到的困难，采用了并行分块消去迭代法，同时在多个处理器上并行计算。得到了较好的结果，并且对进一步开展对三个以上电子体系的关联能并行计算有一定的参考意义。     

范德瓦耳斯和他的状态方程

在物理学发展史上，范德瓦耳斯对气—液流体系统做了开创性的研究工作，建立了人类历史上第一个既能反映气、液各相性质，又能描述相交和临界现象的状态方程。范德瓦耳斯的理论成就和研究方法对热力学、统计力学和低温物理学的发展产生了重要而深远的影响。文章系统探讨了范德瓦耳斯方程产生的历史背景、科学意义和局限性，讨论了范德瓦耳斯的理论和方法对当代物理学的启发意义。     

Broadband laser excitation of van der Waals polymers from a cold atomic gas

In this article, we study the molecular states or polymer states excited from a broadband laser, in which case the dipole blockade will be suppressed. As expected, it is shown that more molecular states are observed through broadband laser excitations compared with narrow-band laser excitations. In addition, it is discovered that a larger energy difference, larger detuning, is required to form deeper potential wells.     

Letter: Brane Cosmology with a van der Waals Equation of State

The evolution of a Universe confined onto a 3-brane embedded in a five-dimensional space-time is investigated where the cosmological fluid on the brane is modeled by the van der Waals equation of state. It is shown that the Universe on the brane evolves in such a manner that three distinct periods concerning its acceleration field are attained: (a) an initial accelerated epoch where the van der Waals fluid behaves like a scalar field with a negative pressure; (b) a past decelerated period which has two contributions, one of them is related to the van der Waals fluid which behaves like a matter field with a positive pressure, whereas the other contribution comes from a term of the Friedmann equation on the brane which is inversely proportional to the scale factor to the fourth power and can be interpreted as a radiation field, and (c) a present accelerated phase due to a cosmological constant on the brane.     

Van der Waals状态方程可压缩多流体流动的PPM方法

基于流体体积分数的混合型多流体数值模型,将Piecewise Parabolic Method（PPM）方法应用于可压缩多流体流动的数值模拟,采用双波近似求解多流体van der Waals状态方程的Riemann问题．模拟高密度比且含有激波的可压缩多流体流动,典型的纯界面平移问题模拟结果表明,在接触间断的界面附近,压力和速度没有任何的振荡且界面数值耗散都被控制在2—3个网格之内;一维和二维算例表明,该数值方法可以有效地处理接触间断、激波和多维滑移线等物理问题,并能够比其它多流体数值方法更精细地模拟多流体交界面．     

Observation of magnetoresistance in CrI3/graphene van der Waals heterostructures

Two-dimensional ferromagnetic van der Waals (2D vdW) heterostructures have opened new avenues for creating artificial materials with unprecedented electrical and optical functions beyond the reach of isolated 2D atomic layered materials, and for manipulating spin degree of freedom at the limit of few atomic layers, which empower next-generation spintronic and memory devices. However, to date, the electronic properties of 2D ferromagnetic heterostructures still remain elusive. Here, we report an unambiguous magnetoresistance behavior in CrI₃/graphene heterostructures, with a maximum magnetoresistance ratio of 2.8%. The magnetoresistance increases with increasing magnetic field, which leads to decreasing carrier densities through Lorentz force, and decreases with the increase of the bias voltage. This work highlights the feasibilities of applying two-dimensional ferromagnetic vdW heterostructures in spintronic and memory devices.     

论范德瓦尔斯a和b参数与温度的关系

范德瓦尔斯方程中a、b参数是否与温度相关,不但不同文献中的说法互不相同,而且有同一文献前后的结论相互矛盾.本文分析了这个令人迷惑的问题.在热力学中a和b参量被处理为与温度无关,它仅仅在临界点附近有效并可以把范德瓦尔斯方程表述为对应态定律;在更加广泛的温度区间a、b参量和温度有关,但是范德瓦尔斯方程却丧失了其独特性.统计...     

Structural and electronic properties of supramolecular C60:RU(II)(bipy)3:C60 triad: Ab initio van der Waals calculations

We have investigated the influence of non-local dispersion interactions and temperature on the structure and electronic properties of Ru(bipy)₃-(C₆₀)₂ triad using the ab initio van der Waals density functional (vdW-DF) calculations. It was found that non-local dispersion interactions affects slightly on the structural geometry and charge transfer property of the system under study. Therefore, it's not necessary to consider dispersion interactions which are computationally more expensive than the conventional DFT calculations for the presented supramolecules.The obtained results from the ab initio MD simulations indicated that structural property of respected molecule varies at various temperatures. The Mulliken charge analyses show a remarkable charge transfer about 0.64 electrons between Ru (bipy)₃-bridges as donors and fullerenes as acceptors entities in the isolated molecule by increasing the temperature, the charge transfer was also increased.Our first-principles results for the isolated complex showed that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) states were located on the fullerene spheroid and thus the charge separation (orbital localization) is not desirable. However, increasing of temperature causes the LUMO's to localize on the acceptor moieties (fullerenes) and the HOMO's on the donor moieties (Ru(bipy)₃). From the results obtained for the molecular orbitals we found that the best distribution is occurred at ambient condition (300 K).     

二维材料的新奇物理及异质结的能带调控

以石墨烯为代表的层状材料具备显著区别于三维材料的新奇物理特性。更为重要的是,原子级平整的二维材料使得科学家们可以将不同的二维材料通过堆垛或者把相同的二维材料通过堆垛加扭转构成范德瓦耳斯异质结。通过层间耦合作用,可对异质结的能带结构和物理性质进行有效调控,从而衍生出单个二维材料所不具备的新奇物性。范德瓦耳斯异质结的能带调控极大地拓宽了二维材料的科学研究和应用前景。     

Surface oxidation in a van der Waals ferromagnet Fe3-xGeTe2

We investigate the surface oxidation in a van der Waals ferromagnet Fe_3-xGeTe₂, a material widely utilized for spintronic applications. While known for its relative air-insensitivity, exposure to air during the handling process (e.g. device or heterostructure fabrication) can lead to reduction or disappearance of its magnetic signal. Comparison of x-ray absorption and x-ray magnetic circular dichroism spectra between pristine and air-exposed Fe_3-xGeTe₂ confirm a naturally oxidized surface layer on the material. The surface oxide layer has predominantly Fe³⁺ content. X-ray absorption spectroscopy done on micron-sized exfoliated Fe_3-xGeTe₂ flakes reveal that the change in the surface chemical properties can be quite significant for thin flakes. The surface modulation of Fe_3-xGeTe₂ can lead to inaccuracies in characterizing its interfacial magnetic and spin transport properties, and complicate device and heterostructure fabrication processes.