液氘单次冲击压缩的QMC模拟研究

液氢在较宽压力与温度范围内具有复杂的物理特性,须从分子层面构建精确模型开展探索研究。利用电子-核耦合的CEIMC法模拟液氘单次冲击实验,分析了液氘冲击特性,当压力达50.3GPa时液氘具有最大压缩率4.48,在110GPa冲击压力附近未发现有压缩率急剧增大的迹象。选用合适的Al基板材料模型,建立了液氘单次压缩状态与实验条件间的关系,总结了单次冲击实验规律。得到的状态方程与现有动高压实验结果一致,也与经修正后的100GPa以上压力的Omega激光实验值吻合,说明采用基于共振价键理论的波函数后,CEIMC法可应用于液氘的冲击模拟。     

共振价键模型中正常态电阻率的讨论

本文运用线性响应理论推导共振价键(RVB)模型中holon-spinon散射和holon-phonon散射导致的正常态电阻率公式。计算结果表明:holon-spinon散射电阻率若用ρ-T^α公式拟合,α在1.4—1.5之间随温度变化;而声子散射电阻率在很大温度范围呈现线性温度行为。 关键词：     

统计自洽场INFERNO模型中电子共振态

对Liberman的统计自洽场INFERNO模型中的电子共振态进行研究,计算金属铀在两个温度密度点处的电子共振态,给出共振能量区间内电子的态密度,波函数,相移因子随能量的变化及位相-振幅形式的波函数中的位相随能量的变化,得到与非相对论情况下完全一致的结果.     

液氘状态方程实验数据测量

在神光Ⅱ高功率激光装置上建立了液氘状态方程实验研究系统, 在80 min内实现控温范围12–300 K可调、控温精度±0.03 K、机械震动 ≤20 μm的实验控制精度; 通过镀膜窗口质量筛选和靶体清洁工作解决了低温下窗口材料残余反射率高的难题, 获得了信噪比较好的实验图像; 利用神光II第九路输出3ω (351 nm)、3 ns、1000 J的能力, 采用阻抗匹配方法, 配合任意反射面速度干涉仪诊断系统, 在国内首次获得液氘在约60 GPa压力下的冲击绝热线实验数据, 数据与国外同压力区间数据符合较好, 为下阶段约100 GPa压力范围液氘状态方程的实验研究奠定了基础.     

BiFeO3晶体价键电子结构与铁电性质的关系

通过价键电子理论工具,计算得到了钙钛矿型单相多铁材料BiFcO₃"赝立方"顺电相和斜方铁电相价键电子结构,分析了价键电子结构变化时其铁电性的影响.计算结果表明,从顺电相到铁电相,BiFeO₃晶胞中各类化学键的键长和价键电子数变化各异,其中Bi-O键键长变短,价键电子数增多,共价性显著增强,对铁电相的稳定起到至关重要的作用;Fe-O键长呈现变大和变小两种结果,价键电子数都减小,共价性减弱.计算结果与第一性原理计算进行了比较.     

弱光场下电子与库仑势散射的微扰解

外光场下电子与库仑势散射的schrodinger 方程可用Floque 分波法分离变量. 径向波动方程是一组无限祸合的二次线性微分方程组, 当弱外光场可视为微扰, 方程组将近似为二次常微分方程并且可积, 由此可得径向波函数、s 矩阵、截面. 无论何种极化或是否作偶极近似,共振谱线是普遍存在的, 井给出共振能量和强度的计算公式. 关键词：     

苝四甲酸二酐薄膜电子结构的同步辐射共振光电子能谱研究

利用基于同步辐射的近边X射线吸收精细结构谱(NEXAFS)和共振光电子谱(RPES)研究了苝四甲酸二酐分子(PTCDA)薄膜的电子结构.碳K边NEXAFS谱中能量小于290 eV的四个峰对应于PTCDA分子不同化学环境碳原子1s电子到未占据分子轨道的共振跃迁.RPES谱中观察到共振光电子发射和共振俄歇电子发射导致的共振峰结构,以及二次谐波激发的碳1s信号.根据电子动能对入射光能量的依赖性分别对三类峰结构进行了归属.同时,发现PTCDA分子轨道共振光电子峰的强度具有光子能量依赖性.这种能量选择性共振增强效应是由于PTCDA分子轨道空间分布差异导致的.共振俄歇峰主要源于高结合能(4.1 eV)分子轨道能级电子参与的退激发过程.明确RPES实验谱图中各个峰结构的起源有助于准确利用基于RPES的芯能级空穴时钟谱技术定量估算有机分子/电极异质界面处电子从分子未占据轨道到电极导带的超快转移时间.     

拓扑相MoS2电子结构及光学性质的第一性原理研究

基于密度泛函理论的第一性原理对二维拓扑相1T′-MoS₂和2M-MoS₂的电子结构、有效质量和光学性质进行研究,并将其与二维H-MoS₂进行对比分析.研究表明,电子有效质量大小关系为：2M-MoS₂22,空穴有效质量大小关系为：T′-MoS₂<2M-MoS₂2,但2M-MoS₂的空穴有效质量和T′-MoS₂相差不大,二者均适用于高性能电子器件.由于拓扑相1T′-MoS₂和2M-MoS₂均存在能带反转,导致带间相关性以及导带和价带的波函数重叠增强,进而光电流响应增强,二者的光学性质均优于H-MoS₂. 2M-MoS₂具有较大的吸收系数和光电导率,2M-MoS₂对红外光和紫外光有着优...     

钙钛矿CaTiO3的超高压结构研究

利用同步辐射x射线衍射和 DAC 高压技术在室温下测量了钙钛矿CaTiO₃在压力0—44.53 GPa下的结构变化.结果表明，随着压力的增加CaTiO₃的三个晶轴都受到不同程度的压缩，a,b的压缩率相近且相对比较大，c的压缩率最小，但没有证据表明有相变的发生.在压力范围内CaTiO₃的P-V关系用Murnaghan状态方程表示，设定K′0=4，得到V0=0.2245(6)nm3和K0=222(9) GPa.应用赝立方角γpc与压力的关系，初 关键词： 3')" href="#">CaTiO₃ 结构 超高压 状态方程     

单粒子共振态的实稳定方法研究

基于实稳定方法的基本思想，在坐标空间求解了一维势阱和三维球对称势阱中的单粒子共振态，得到的共振能量、宽度和波函数等与散射相移法以及耦合常数的解析延拓方法的结果一致. 关键词： 共振态 实稳定方法 相移 共振宽度     

Fate of the resonating valence bond in graphene

We apply a variational wave function capable of describing qualitatively and quantitatively the so-called "resonating valence bond" (RVB) in realistic materials, by improving standard ab initio calculations by means of quantum Monte Carlo methods. In this framework we clearly identify the Kekulé and Dewar contributions to the chemical bond of the benzene molecule and establish the corresponding RVB energy of these structures (?0.01 eV/atom). We apply this method to unveil the nature of the chemical bond in undoped graphene, providing an estimate of the RVB energy gain, and show that this picture remains only within a small "resonance length" of a few atomic units.     

Benchmarking vdW‐DF first‐principles predictions against Coupled Electron–Ion Monte Carlo for high‐pressure liquid hydrogen

We report first‐principles results for the nuclear structure and optical responses of high‐pressure liquid hydrogen along two isotherms in the region of molecular dissociation. We employ density functional theory with the vdW‐DF approximation (vdW) and benchmark the results against existing predictions from Coupled Electron–Ion Monte Carlo (CEIMC). At fixed density and temperature, we find that the pressure obtained from vdW is higher than that from CEIMC by about 10 GPa in the molecular insulating phase and about 20 GPa in the dissociated metallic phase. Molecules are found to be over‐stabilized using vdW, with a slightly shorter bond length and with a stronger resistance to compression. As a consequence, pressure dissociation along isotherms using vdW is more progressive than that computed with CEIMC. Below the critical point, the liquid–liquid phase transition is observed with both theories in the same density region, but the one predicted by vdW has a smaller density discontinuity, i.e. a smaller first‐order character. The optical conductivity computed using Kubo–Greenwood formulation is rather similar for the two systems and reflects the slightly more pronounced molecular character of vdW.     

Phase coherence of RVB wave function

We establish the phase coherence of a variational resonating valence bond (RVB) wave function in the case of nearest neighbor singlets on a square lattice in the fermion representation. The result applies both in the half filled band case and in the doped case.     

Resonating valence bond states in doped square-lattice antiferromagnets: finite cluster calculations

We discuss some general features of the resonating valence bond (RVB) ansatz for the ground state of quantums=1/2 Heisenberg antiferromagnets (AFMs). For finite clusters of up to 16 spins on the square lattice we compare the exact ground state with a short-range correlated RVB trial wave function. Since in the pure square-lattice AFM the short-range correlated RVB state differs significantly from the real ground state we discuss different mechanisms that favour the RVB state. In particular, we study the influence of anisotropy, disorder and frustration, which could be relevant for slightly doped high-T _c superconducting materials. Furthermore, we discuss the influence of holes on the realization of a RVB state. We found that exchange disorder and, in particular, frustration and holes can favour a short-range correlated magnetic state, which is well described by a RVB state.     

Coupling static and dynamic compressions: first measurements in dense hydrogen

We demonstrate here a laser-driven shock wave in a hydrogen sample, pre-compressed in a diamond anvil cell. The compression factors of the dynamic and static techniques are multiplied. This approach allows access to a family of Hugoniot curves which span the P–T phase diagram of fluid hydrogen to high density. In this first-of-its-kind experiment, two hydrogen Hugoniot curves have been partially followed starting from pre-compression at pressures of 0.7?GPa and 1.2?GPa. Optical reflectance probing at two wavelengths reveals the onset of the conducting fluid state. The boundary line to conducting fluid hydrogen is suggested.     

Use of a wave reverberation technique to infer the density compression of shocked liquid deuterium to 75 GPa

A novel approach was developed to probe density compression of liquid deuterium (L-D2) along the principal Hugoniot. Relative transit times of shock waves reverberating within the sample are shown to be sensitive to the compression due to the first shock. This technique has proven to be more sensitive than the conventional method of inferring density from the shock and mass velocity, at least in this high-pressure regime. Results in the range of 22-75 GPa indicate an approximately fourfold density compression, and provide data to differentiate between proposed theories for hydrogen and its isotopes.     

d-Wave resonating valence bond states of fermionic atoms in optical lattices

We study controlled generation and measurement of superfluid d-wave resonating valence bond (RVB) states of fermionic atoms in 2D optical lattices. Starting from loading spatial and spin patterns of atoms in optical superlattices as pure quantum states from a Fermi gas, we adiabatically transform this state to an RVB state by a change of the lattice parameters. Results of exact time-dependent numerical studies for ladders systems are presented, suggesting generation of RVB states on a time scale smaller than typical experimental decoherence times.     

Electrical resistivity of fluid methane multiply shock compressed to 147 GPa

Shock wave experiments were carried out to measure the electrical resistivity of fluid methane. The pressure range of 89–147?GPa and the temperature range from 1800 to 2600?K were achieved with a two-stage light-gas gun. We obtained a minimum electrical resistivity value of 4.5?×?10^?2?Ω?cm at pressure and temperature of 147?GPa and 2600?K, which is two orders of magnitude higher than that of hydrogen under similar conditions. The data are interpreted in terms of a continuous transition from insulator to semiconductor state. One possibility reason is chemical decomposition of methane in the shock compression process. Along density and temperature increase with Hugoniot pressure, dissociation of fluid methane increases continuously to form a H₂-rich fluid.     

Electronic model for CoO2 layer based systems: chiral resonating valence bond metal and superconductivity

Takada et al. have reported superconductivity in layered Na(x)CoO(2)yH(2)O (T(c) approximately equal to 5 K). We model a reference neutral CoO2 layer as an orbitally nondegenerate spin-1/2 antiferromagnetic Mott insulator on a triangular lattice and Na(x)CoO(2)yH(2)O as electron doped Mott insulators described by a t-J model. It is suggested that at optimal doping chiral spin fluctuations enhanced by the dopant dynamics lead to a gapful d-wave superconducting state. A chiral resonating valence bond (RVB) metal, a parity and time (PT) reversal violating state with condensed RVB gauge fields, with a possible weak ferromagnetism, and low temperature p-wave superconductivity are also suggested at higher dopings.