几类粒子密度算符和粒子流密度算符的讨论

从粒子密度和粒子流密度出发,分析了几类相关的算符,讨论了它们的性质与相互关系;从具体的物理意义出发,明确了合适的粒子密度算符和粒子流密度算符的表达形式.     

曲率对Rh在锯齿型单壁碳纳米管内外吸附影响的研究

利用密度泛函理论系统的研究了单壁碳纳米管的曲率对Rh原子在锯齿型碳管内外的吸附行为, 发现Rh原子在管外吸附比管内稳定; 随着碳管管径的增加, 曲率减小, 管内外吸附能的差值逐渐减小, 接近Rh原子在石墨烯上的吸附能. 电荷密度分析表明, 由于卷曲效应使碳纳米管管外的电荷密度大于管内, 随着曲率减小, 这种差别逐渐减小. 管内外吸附Rh原子的Bader电荷差值及局域态密度差别亦随着曲率的下降而减小, 这与Rh原子在管内外吸附能的变化规律相一致.     

Universality principle and the development of classical density functional theory

The universality principle of the free energy density functional and the ‘test particle' trick by Percus are combined to construct the approximate free energy density functional or its functional derivative. Information about the bulk fluid radial distribution function is integrated into the density functional approximation directly for the first time in the present methodology. The physical foundation of the present methodology also applies to the quantum density functional theory.     

Density Matrix in Quantum Mechanics and Distinctness of Ensembles Having the Same Compressed Density Matrix

We clarify different definitions of the density matrix by proposing the use of different names, the full density matrix for a single-closed quantum system, the compressed density matrix for the averaged single molecule state from an ensemble of molecules, and the reduced density matrix for a part of an entangled quantum system, respectively. We show that ensembles with the same compressed density matrix can be physically distinguished by observing fluctuations of various observables. This is in contrast to a general belief that ensembles with the same compressed density matrix are identical. Explicit expression for the fluctuation of an observable in a specified ensemble is given. We have discussed the nature of nuclear magnetic resonance quantum computing. We show that the conclusion that there is no quantum entanglement in the current nuclear magnetic resonance quantum computing experiment is based on the unjustified belief that ensembles having the same compressed density matrix are identical physically. Related issues in quantum communication are also discussed.     

也谈概率密度和概率流密度算符

针对<大学物理>2008年第8期上关于粒子概率密度算符和概率流密度算符的讨论一文进行了补充,对一般空间(如动量空间)中的概率和概率流进行了较系统的阐述,并纠正了该文中的有关错误论断.     

A Further Generalized Lagrangian Density and its Special Cases

By summarizing and extending the Lagrangian densities of general relativity and the Kibble’s gauge theory of gravitation,a further generalized Lagrangian density for a gravitational system is obtained and analyzed in greater detail, which will extend the studying range for the theory of gravitation. Many special cases can be derived from this generalized Lagrangian density, and the general characteristics and some peculiarities of them will be described and discussed.     

量子力学中的密度矩阵与具有相同密度矩阵的系综的可区分性

讨论了密度矩阵的不同定义。建议使用完全密度矩阵、压缩密度矩阵和约化密度矩阵分别描写一个封闭量子体系的、一个系综中平均分子的和一个复合体系中的一个子系统的密度矩阵。强调这与现在人们认为的具有相同压缩密度矩阵的系综是完全等价的结论完全不同,具有相同压缩密度矩阵但是成分不同的系综可以通过系综整体测量来区别。作为一个应用,现在认为现有的核磁共振量子计算中没有纠缠的结论是没有根据的。Density matrix is one important tool in quantum mechanics, and it has very broad applications. However there are different definitions about the density matrix, and they describe quite different systems. There has been some misunderstanding about the density matrix in the community, and these misunderstandings hinder the right application of the density matrix. In this article, we discuss the different definitions of density matrix. We suggest to use the full density matrix, compressed density matrix and the reduced density matrix to describe the state of a complete quantum system, the state of an averaged particle in an ensemble and the state of part of a composite system. We stress that contrary to the wide accepted understanding that ensembles with the same compressed density matrix are physically indistinguishable, they are distinguishable through the so-called ensemble measurement. As an application, we suggest that the present conclusion that the present-day nuclear magnetic resonance quantum computation does not have quantum entanglement is groundless.     

Electronic structure of twinned ZnS nanowire

The electronic properties of twinned ZnS nanowires （NWs） with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal （2H） stacking inside the cubic （3C） stacking has no effect on the electronic properties of thin ZnS NWs.     

Electronic structure of twinned ZnS nanowires

The electronic properties of twinned ZnS nanowires (NWs) with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal (2H) stacking inside the cubic (3C) stacking has no effect on the electronic properties of thin ZnS NWs.     

介质损耗与电磁能量

根据能流密度公式,推出时谐场中存在线性有损介质情形的坡印亭定理.与能量守恒定律结合,得到极化损耗、磁化损耗和焦耳损耗功率密度公式,以及有损介质中的电磁场能量密度公式.最后,推出上述各量的平均值公式.     

Probability and Joint Probability Distributions for Systems Driven by Correlated Colored Noises

This paper deals with systems driven by correlated colored noises. The evolution equations for both the single and joint probability distribution functions are derived. It is shown that both the stationary and dynamical properties of the systems are affected by correlated colored noises. These results are obtained by means of the systematic use of the ordered cumulant-expansion technique.     

HMO model of scalar field in vacuum

In this paper, the HMO model of scalar field in vacuum is developed using the covariant field theory, in which the so-called current density and mass density of optical fluid are obtained and analyzed.     

HMO model of scalar field in vacuum

In this paper, the HMO model of scalar field in vacuum is developed using the covariant field theory, in which the so-called current density and mass density of optical fluid are obtained and analyzed.     

高温超导电机电枢线圈临界电流密度研究

高温超导线材的临界电流密度受磁场的影响,在设计计算时,通常假设在线圈截面上电流密度是均匀分布的。但是,实际上在线圈截面上,电压是一致的。由于线圈中的磁场不均匀分布,各处的临界电流密度是不同的。采用数值模拟的方法,分析了高温超导线圈截面上的临界电流分布。结果显示,临界电流密度的分布是不均匀的,总的临界电流可比按均匀分布时的计算结果提高25%以上。     

原子核壳模型单体密度矩阵的数值计算

提出平均场壳模型下原子核单体密度矩阵的一种计算方法,验证该方法的可靠性.计算双幻核⁴⁰Ca,⁹⁰Zr的单体密度矩阵,利用单体密度矩阵计算核子密度分布和动量分布,并分别与Hartree-Fock-Bogolubov理论结果、定域费米气体模型结果以及实验数据进行比较.     

非迭代冻结密度近似方法在计算氢键相互作用的合理性研究

为计算相互作用较弱的分子碎片之间的耦合能,Harris从密度泛函理论出发,提出了一种简化方法,即冻结密度近似(FDA)方法.对该方法在描述分子间氢键作用的合理性进行了验证.对水分子间的HO┉H氢键、甲酰胺与水分子间的NH┉O氢键、二氟甲烷和水分子间的OH┉F氢键,以及DNA中的碱基(AT,GC)之间的N—H┉O,N—H┉N等类型的氢键的计算表明:若电子交换关联采用非定域自旋密度近似,FDA的计算结果同其他abinitio方法的计算结果以及实验结果都符合得很好.FDA在计算过程中既不需要求解泊松方程,也不需要进行反复的自洽迭代,所以运算速度较快,在研究生物大分子体系中的氢键相互作用方面具有一定的使用价值 关键词： 冻结密度近似 氢键 密度泛函     

Augmented Kierlik--Rosinberg Fundamental Measure Functional and Extension of Fundamental Measure Functional to Inhomogeneous Non-hard Sphere Fluids

From point of view of weighted density procedure, it is guessed that a Percus-Yevick （PY） compressibility excess free energy density, appearing in the Kierlik Rosinberg type fundamental measure functional （KR-FMF） and expressed in terms of scaled particle variables, can be substituted by a corresponding expression dictated by a more accurate Mansoori Carnahan-Starling Leland （MCSL） equation of state, while retaining the original weighting functions; it is numerically indicated that the resultant undesirable non-self-consistency between the PY type weighting function and MCSL type excess free energy density had no bad effect on the performance of the resultant augmented KR-ffMF which, on the one hand, preserves the exact low-density limit of the original KR-FMF and holds a high degree of pressure self-consistency, on the other hand, improves significantly, as expected, the predictions of density profile of hard sphere fluid at single hard wall contact location and its vicinity, and of the bulk hard sphere second order direct correlation function （DCF）, obtained from functional differentiation. The FMF is made applicable to inhomogeneous non-hard sphere fluids by supplementing a functional perturbation expansion approximation truncated at the lowest order with summation of higher order terms beyond the lowest term calculated by the FMF for an effective hard sphere fluid; the resultant extended FMF only needs second order DCF and pressure of the fluid considered at coexistence state as inputs, consequently is applicable whether the considered temperature is above critical point or below critical point. The extended MCSL-augmented KR-FMF is found to be endowed with an excellent performance for predictions of density profile and surface tension by comparing the present predictions of these two quantities with available computer simulation data for inhomogeneous hard core attractive Yukawa fluid and Lennard-3ones fluid.     

Specification of Density Functional Approximation by Radial Distribution Function of Bulk Fluid

A systematic methodology is proposed to deal with the weighted density approximation version of classical density functional theory by employing the knowledge of radial distribution function of bulk fluid.The present methodology results from the concept of universality of the free energy density functional combined with the test particle method.It is shown that the new method is very accurate for the predictions of density distribution of a hard sphere fluid at different confining geometries.The physical foundation of the present methodology is also applied to the quantum density functional theory.     

半导体性单壁碳纳米管与其石墨衬底表面相互作用的第一性原理计算

利用基于密度泛函理论的计算方法,研究了处于石墨（HOPG）表面的半导体性单壁碳纳米管,发现碳纳米管下面的石墨受碳管的作用向下凹陷,而纳米管本身虽然保持其形状不变,但它的电子态受石墨衬底影响,造成导带下移,禁带宽度明显减小. 关键词： 单壁碳纳米管 密度泛函理论 局域密度近似方法     

Harmonic analysis of Mössbauer spectra and its applications

Summary A new iterative procedure for a numerical analysis of M?ssbauer spectra in terms of higher-order harmonics is used to study spin-and charge-density waves in single-crystal and polycrystalline samples of chromium and chromium-vanadium alloys. Paper presented at the ICAME-95, Rimini, 10–16 September 1995