Compton profile of tantalum

The Compton profile of tantalum (Ta) has been measured using IGP type coaxial photon detector. The target atoms were excited by means of 59.54 keV γ-rays from Am-241. The measurements were carried out on a high purity thin elemental foil. The data were recoreded in a 4 K multichannel analyzer. These data duly corrected for various effects are presented and compared with theoretical and measured values. Best agreement with experiment is found for the 5d³6s² electron configuration     

Compton profile study of α-manganese

The results of a Compton profile study on polycrystallineα-Mn are reported. Our measurement are compared with theoretical results computed for different 3d-4s electron configurations within the RFA model. Best agreement between the measured and calculated values is found for 3d ^5·44s ^1·6 configuration. Theoretical Compton profile ofγ-Mn calculated using the same procedure is close to that for bcc phase with similar electron configurations.     

Optimization of deconvolution in Compton profile measurements

The method of generalized least squares has been used to deconvolute the Compton profile measurements in nickel. The method depends on two arbitrary parameters namely the cut-off parameterK and the damping factor λ. This has been discussed and a method suggested to optimize the damping parameter.     

Compton profile of molybdenum

In this paper we report the experimental Compton profile of polycrystalline molybdenum. The measurements have been made by scattering 59.54 keVγ-rays and are compared with the recent band structure calculation of Janiet al. [4]. These results have also been compared with our calculation based on the renormalized-free-atom model for different 4d-5s configurations. It is found that the present experimental data are relatively in good agreement with the band structure calculation.     

MgS和MgSe带隙的GW近似修正

应用基于密度泛函理论下的局域密度近似（DFT-LDA）方法研究了岩石矿结构的 MgS和MgSe的晶体结构和能带结构。本文得到稳定结构的晶格常数与已知实验数据相吻合,MgS和MgSe都是间接带隙半导体且带隙值分别为2.74 eV和1.70 eV。尽管本文利用LDA计算的带隙值与之前的理论值很接近,但是局域密度近似常常低估带隙值。因此应用准粒子GW（G是格林函数,W是库伦屏蔽相互作用）近似 对MgS和MgSe的带隙值进行了修正,其结果分别为4.15eV和2.74 eV。GW近似的结果应该是合适的值。     

Structural,electronic and optical properties of cubic SrTiO3 and KTaO3: Ab initio and GW calculations

We present first-principles VASP calculations of the structural, electronic, vibrational, and optical properties of paraelectric SrTiO₃ and KTaO₃. The ab initio calculations are performed in the framework of density functional theory with different exchange-correlation potentials. Our calculated lattice parameters, elastic constants, and vibrational frequencies are found to be in good agreement with the available experimental values. Then, the bandstructures are calculated with the GW approximation, and the corresponding band gap is used to obtain the optical properties of SrTiO₃ and KTaO₃.     

MgS和MgSe带隙的GW近似修正

应用基于密度泛函理论下的局域密度近似（DFT-LDA）方法研究了岩石矿结构的 MgS和MgSe的晶体结构和能带结构。本文得到稳定结构的晶格常数与已知实验数据相吻合,MgS和MgSe都是间接带隙半导体且带隙值分别为2.74 eV和1.70 eV。尽管本文利用LDA计算的带隙值与之前的理论值很接近,但是局域密度近似常常低估带隙值。因此应用准粒子GW（G是格林函数,W是库伦屏蔽相互作用）近似 对MgS和MgSe的带隙值进行了修正,其结果分别为4.15eV和2.74 eV。GW近似的结果应该是合适的值。     

Electronic structure of ScN and YN： density-functional theory LDA and GW approximation calculations

The desirable physical properties of hardness, high temperature stability, and conductivity make the early transition metal nitrides important materials for various technological applications. To learn more about the nature of these materials, the local-density approximation(LDA) and GW approximation i.e. combination of the Green function G and the screened Coulomb interaction W, have been performed. This paper investigates the bulk electronic and physical properties of early transition metal mononitrides, ScN and YN in the rocksalt structure. In this paper, the semicore electrons are regarded as valance electrons. ScN appears to be a semimetal, and YN is semiconductor with band gap of 0.142eV within the LDA, but are in fact semiconductors with indirect band gaps of 1.244 and 0.544\,eV respectively, as revealed by calculations performed using GW approximation.     

Renormalized-free-atom model and Compton profile of hcp cobalt

Compton profile of cobalt has been calculated employing the renormalized-free-atom model for fcc as well as hcp phases choosing several 3d-4s configurations. The results have been compared with recent gamma-ray measurements on polycrystalline Co. Best agreement between theory and experiment is found for 3d ⁷4s ² configuration. Comparison with free electron model has also been made for this case.     

On the use of Fourier-transformed Compton profile for the determination of band occupancies in certain solids

The Pattison-Williams method of using Fourier-transformed Compton profiles for obtaining Fermi momenta in simple metals, is extended to set up a scheme for inferringd orf band occupancies in transition metals, rare earths etc. CP measurements are reported for Ni,α-Mn andβ-Mn and then the new scheme is applied to obtain 3d occupancies in these systems. Some comments on the use of this method for other systems are also made.     

Compton profile study of V3Ge and Cr3Ge

In this paper the results of a Compton profile study of two polycrystalline A15 compounds, namely, V₃Ge and Cr₃Ge, have been reported. The measurements have been performed using 59.54 keV γ-rays from an ²⁴¹Am source. The theoretical Compton profiles have been computed for both the compounds using ab-initio linear combination of atomic orbitals (LCAO) method employing CRYSTAL98. For both the A15 compounds, the isotropic experimental profiles are found to be in good overall agreement with the calculations. The comparison points out residual differences in V₃Ge whereas for Cr₃Ge the differences are within experimental error. The behaviour of valence electrons in the two iso-structural compounds has been examined on the scale of Fermi momentum. The valence electron distribution seems to be dominated by the metallic constituents rather than Ge and two compounds show covalent nature of bonding which is larger in V₃Ge compared to Cr₃Ge.      

浅析影响康普顿谱线位置的因素

康普顿散射中影响康普顿谱线位置的因素是十分复杂的,文章主要针对影响康普顿谱线位置的几个因素作了理论探讨,得出影响因素主要在于:电子具有初速度会增大散射波长的改变量;束缚能的存在要减小峰值波长的改变量;双光子散射和二次散射与谱线峰值位置的关系不大,二者对峰值波长的改变是不确定的、复杂的、在连续的范围内变化的.最后对康普顿谱线位置和康普顿轮廓的理论研究和应用前景作了展望.     

Electronic and optical properties of ceramic Sc2O3 and Y2O3: Compton spectroscopy and first principles calculations

We present the first-ever experimental Compton profiles (CPs) of Sc₂O₃ and Y₂O₃ using 740 GBq ¹³⁷Cs Compton spectrometer. The experimental momentum densities have been compared with the theoretical CPs computed using linear combination of atomic orbitals (LCAO) within density functional theory (DFT). Further, the energy bands, density of states (DOS) and Mulliken's population (MP) data have been calculated using LCAO method with different exchange and correlation approximations. In addition, the energy bands, DOS, valence charge density (VCD), dielectric function, absorption coefficient and refractive index have also been computed using full potential linearized augmented plane wave (FP-LAPW) method with revised functional of Perdew–Becke–Ernzerhof for solids (PBEsol) and modified Becke Johnson (mBJ) approximations. Both the ab-initio calculations predict wide band gaps in Sc₂O₃ and Y₂O₃. The band gaps deduced from FP-LAPW (with mBJ) are found to be close to available experimental data. The VCD and MP data show more ionic character of Sc₂O₃ than Y₂O₃. The ceramic properties of both the sesquioxides are explained in terms of their electronic and optical properties.     

原子康普顿轮廓的解析计算

利用变分原理和冲量近似,给出了原子康普顿轮廓的解析计算方法。基于该方法具体导出了第一和第二周期元素各轨道电子的康普顿轮廓解析表达式,并绘制了各轨道电子的康普顿轮廓在Q=0-4范围内的变化情况。通过与文献结果的比较,验证了本文计算方法和结论的可靠性。     

原子康普顿轮廓的解析计算

利用变分原理和冲量近似,给出了原子康普顿轮廓的解析计算方法 .基于该方法具体导出了第一和第二周期元素各轨道电子的康普顿轮廓解析表达式,并绘制了各轨道电子的康普顿轮廓在Q=0-4范围内的变化情况.通过与文献结果的比较,验证了本文计算方法和结论的可靠性.     

Electron momentum density and Compton profile by a semi-empirical approach

Here we propose a semi-empirical approach to describe with good accuracy the electron momentum densities and Compton profiles for a wide range of pure crystalline metals. In the present approach, we use an experimental Compton profile to fit an analytical expression for the momentum densities of the valence electrons. This expression is similar to a Fermi–Dirac distribution function with two parameters, one of which coincides with the ground state kinetic energy of the free-electron gas and the other resembles the electron–electron interaction energy. In the proposed scheme conduction electrons are neither completely free nor completely bound to the atomic nucleus. This procedure allows us to include correlation effects.We tested the approach for all metals with Z=3–50 and showed the results for three representative elements: Li, Be and Al from high-resolution experiments.     

Compton scattering study and electronic properties of vanadium carbide: A validation of hybrid functional

In this paper, we have reported the isotropic Compton profile of VC measured using high energy (661.65 keV) γ-radiations from a ¹³⁷Cs isotope. To compare the experimental momentum densities, we have also employed the linear combination of atomic orbitals (LCAO). In addition, energy bands, density of states and Fermi surface topology of VC have been computed using FP-LAPW and LCAO methods. It is seen that the LCAO with hybridization of density functional theory and Hartree-Fock (so called B3LYP) gives a better agreement with the present Compton profile experiment. This shows validation of an exact exchange part in hybrid density functional. On the basis of energy bands, we have discussed the microscopic origin for the anomalous behavior of hardness of VC. The relative nature of bonding in VC and NbC is also discussed in terms of valence charge densities and Mulliken′s population analysis. To establish the role of Compton profiles in computation of cohesive properties of refractory materials, we have also calculated for the first time the cohesive energy using the present experimental Compton profile and compared it with the existing data.     

Cr掺杂ZnSe团簇稳定性和磁性质

本文采用密度泛函理论研究了Cr原子单掺杂和双掺杂(ZnSe)_(12)团簇的结构、电子性质和磁性质.考虑了三种掺杂方式:替代掺杂,外掺杂和内掺杂.单掺杂时,外掺杂团簇是最稳定结构,而对于双掺杂,内掺杂团簇是最稳定结构.团簇磁矩主要来自Cr-3d态的贡献,4s和4p态也贡献了一小部分磁矩.由于轨道杂化,相邻的Zn和Se原子上也产生少量自旋.结果显示Cr原子间的磁性耦合是短程相互作用.     

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     

Fe掺杂ZnSe团簇结构和磁性质

采用密度泛函理论研究了Fe原子单掺杂和双掺杂(ZnSe)12团簇的结构、电子性质和磁性质.我们考虑了三种掺杂方式:替代掺杂,外掺杂和内掺杂.单掺杂时,外掺杂团簇是最稳定结构;而双掺杂时,内掺杂团簇是最稳定结构.团簇磁矩主要来自Fe-3d态的贡献,4s和4p态也贡献了一小部分磁矩.由于轨道杂化,相邻的Zn和Se原子上也产生少量自旋.不同掺杂团簇的总磁矩不同,在可调磁矩的磁性材料领域有潜在应用价值.