Fourier transformed Compton profiles of semiconductors

The Fourier transformed Compton profiles of several semiconductors are calculated by using a set of realistic Wannier functions. The results obtained in silicon, where experimental information exists, are used to test the one-electron approximation. The study of a series of semiconductors shows the effect of their electronic structure on the Compton scattering.     

Determination of Fermi momentum using Fourier transformed Compton profile

We examine the effect of electron correlations on the Fourier transformed Compton profile (FTCP) and on the use of FTCP for determining the Fermi momentum.     

Comments on reconstruction of Fermi surface from high-resolution Compton data

A few comments are made on reconstruction of three-dimensional (3D) momentum density and Fermi surface mapping from high-resolution Compton data. Equivalence of LCW-folding and Schuelke's method in converting observed momentum density to occupation number density is explicitly shown.     

Molecular Compton profiles from SCF-MO wavefunctions

Compton profiles are derived from ab initio SCF-MO wavefunctions calculated for cyclopropane, propene, aziridine, ethanimine, ethenamine, oxirane, acetaldehyde and formamide using Dunning's gaussian orbital basis. Good agreement with the experimental profile is found for formamide. The differences between the profiles for the cyclic and acyclic isomers are only slightly larger than the experimental accuracy that can presently be achieved. The cyclic compounds have slightly broader profiles and there are no significant differences arising from strain. Comparison with profiles derived from localized orbital contributions indicate that the localized orbital approach is essentially valid for these systems.     

Molecular Compton profiles from SCF-MO wavefunctions

This paper considers the dependence of Compton profiles calculated from molecular wavefunctions on the atomic basis set used. For fluoromethane there is no significant difference between profiles calculated with a Slater minimal basis set and with STO-3G, STO-4G and STO-5G sets. A Slater double-zeta set and Dunning's gaussian basis give essentially the same profile and the addition of polarization functions to the Dunning basis has little effect. For methanol, methylamine and ethane there is a significant difference between the STO-3G profiles and those calculated from extended basis sets but again the addition of polarization functions has little effect. The use of Dunning's basis would seem to be adequate for Compton profile calculations for molecules of medium size. As one goes along the series from ethane to fluoromethane the Compton profile becomes broader.     

Compton profiles and nesting of Fermi surfaces for B2-TiNi and B2-TiPd

The band structures of the shape memory alloys B2-TiNi and B2-TiPd are calculated by the full potential linearized augmented plane wave method with the local density approximation. The theoretical Compton profiles for B2-TiNi and B2-TiPd are calculated. In addition, the three-dimensional (3D) occupation number densities obtained by Lock-Crisp-West (LCW) analysis are presented for the first time. These 3D occupation number densities are in good agreement with the Compton scattering experiment for TiNi. Both shape memory alloys are based on martensitic transformation, which is caused by soft phonons. The charge-density wave is created by nesting of Fermi surfaces, which leads to phonon softening. To examine the nesting vectors quantitatively, we calculate the generalized susceptibility χ(q). χ(q) shows peaks at 0.315[110]2π/a and 0.4[111]2π/a for TiNi and at 0.275[110]2π/a and 0.395[111]2π/a for TiPd. Although the nesting vector in the [110] direction agrees with that from the phonon experiment, the nesting vector in the [111] direction differs from that in the experimental results.     

Fermi surface parameters of graphite by band calculations

Energy bands near the Fermi surface of graphite are calculated by a new method suitable for layer-type crystals. Theoretical values for the band parameters in the Slonczewski-Weiss band model are obtained, and they are in good agreement with experimental ones.     

Derivation of the radial distribution function from experimental Compton profiles

The analysis of experimental Compton profiles in position rather than momentum space provides a useful method of interpreting Compton data. A density matrix approach is employed to establish the relationship between the Compton profile J(p), and the Fourier transform of the momentum density B(r), and, for a homogeneous system, the radial distribution function g(r). An earlier Compton profile measurement on sodium provides the data for a demonstration of the long range charge correlations in a metal, in analogy with the Friedel oscillations in a screening charge.     

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.     

New reconstruction method of electron momentum densities from Compton profiles

Recent advances in Compton scattering experiments have led to renewed interest in reconstructing three-dimensional electron momentum densities from Compton profiles. We present a new reconstruction method based on the inversion of the Radon transform in terms of spherical harmonics and Jacobi polynomials. This technique is demonstrated on model projections having the hexagonal symmetry. Reconstructed densities, being in very good agreement with the model ones, are a very good performance of this new algorithm.     

Compton profiles of trigonal and amorphous selenium

Compton profiles of trigonal and amorphous Selenium were measured with ²⁴¹Am γ-radiation using two crystalline and amorphous samples of identical geometric dimensions. As a result the difference profiles of amorphous and polycrystalline Se are reported and discussed. The valence electron Compton profile of the polycrystalline phase is compared to SCOPW-calculations by Krusius.     

Compton profiles of multiply ionized oxygen atoms

We have calculated Compton profiles of multiply ionized oxygen atoms with electronic configurations 1s^m2sⁿ2p^q, m=1−2,n=0−2,q=0−4. The values of the Compton profiles from the present calculation can be used to determine the doubly differential electron production cross sections in recent ion-atom collision experiments with oxygen ions in the rest frame of the target atoms. The calculations have been performed in impulse approximation using numerical Hartree-Fock wave functions. Compton profiles of neutral oxygen atoms, available in the literature, are in excellent agreement with the present calculation. The variation of Compton profile with the degree of ionization is investigated.     

Fermi surface of LaAg

Electronic structure, especially the Fermi surface, is calculated for the intermetallic rare-earth compound LaAg, known to show the structural phase transition when In is substituted for Ag, by a self-consistent fully-relativistic APW method with the exchange-correlation potential in a local-density approximation. The Fermi surface is found to consist of large hole and electron sheets as well as small hole and electron sheets. This result confirms well the theoretical prediction by Niksch et al. (1987). These Fermi surface sheets are found to explain the experimental results for the de Haas-van Alphen effect by Niksch et al. (1987) and Motoki et al. (1995) reasonably well. But, the frequency branches originating from the large hole sheet have been observed only partially. Local curvature of the large hole sheet is investigated as a possible origin of the disappearance of these frequency branches.     

Fermi surface of the noble metals

We report calculations of extremal areas of four Fermi surface (FS) orbits of the noble metals using the linear muffin tin orbital method in the atomic sphere approximation. Our calculations indicate that thel = 3 potential parameters and increase in the number of k-points in the Brillouin zone (BZ) summation from 240 to 916 have no significant effect on the FS. All calculations were performed self-consistently including up tol = 2 potential parameters and with 240 k points in the BZ summation. Calculations were performed with the exchange, correlation potentials (XCP) of Barth-Hedin, Barth-Hedin modified by Janak, SlaterX _α, and the Vosko-Wilk-Nussair. Results compared with other theoretical calculations indicate that none of the above XC potentials give an accurate representation of the FS for all the noble metals. We feel that the inclusion of the non-locality of XCP may give a better account of the FS geometry.     

Momentum densities and Compton profiles of alkali-metal atoms

It is assumed that the dynamics of valence electrons of alkali-metal atoms can be well accounted for by a quantum-defect theoretic model while the core electrons may be supposed to move in a self-consistent field. This model is used to study the momentum properties of atoms from³Li to³⁷Rb. The numerical results obtained for the momentum density, moments of momentum density and Compton profile are found to be in good agreement with the results of more detailed configuration-interaction calculations for the atom³Li. Similar results for¹¹Na,¹⁹K and³⁷Rb are compared with the corresponding Hartree-Fock-Roothaan values only, for want of data from other realistic calculations