The authors present self-consistent band-structure calculations of HCP Be made by means of the full-potential linearised-augmented-plane-wave (LAPW) method and on the basis of the local density approximation. In contrast to earlier calculations no shape approximations for the charge density or the potential are made and all electrons are taken into account. From the full charge density, X-ray form factors are calculated that agree very well with recent experimental data. This indicates that the significant deviations between experiment and earlier calculations are due to strong muffin-tin- effects. The electric field gradient (EFG) is very sensitive to the quality of the theoretical calculation. In earlier theoretical work not even the sign of the EFG could be determined unambiguously. Within the authors formalism the EFG is determined directly from a given charge density without any approximations. Starting with a muffin-tin potential the EFG is found to be 15 times larger than experiment. The present full-potential LAPW calculation, however, yields an EFG in good agreement with experiment. From calculations at different lattice constants it is found that the EFG depends strongly on the c/a ratio but only weakly on the volume. The equilibrium lattice parameters are determined by total-energy minimisation and agree with experiment within 2%.

A full-potential LAPW study of structural and electronic properties of beryllium

The composite wave variational version of the APW method has been used in conjunction with the LCAO interpolation scheme to compute the energy bands and the joint density of states of the compounds BeS, BeSe and BeTe at various symmetry points and axes of the Brillouin zone. From these computed bands, all three materials are found to be semiconductors having band gaps of 6.10 eV, 4.75 eV and 1.49 eV, respectively. From the joint density of state characteristics, various optical transitions have also been predicted. The results have been favourably compared with those of Stukel. Since BeTe is found to be a small-gap semiconductor, its possible technological importance has also been emphasised.

https://iopscience.iop.org/article/10.1088/0022-3719/10/1/011/pdf

Electronic energy bands of BeS, BeSe and BeTe

Electronic structures for Mg, Zn and Cd have been completed using the linear muffin tin orbital method. The results include plots of band structure, Fermi-surfaces in extended and reduced zone schemes and density-of-states functions. Generally, good agreement with some other ab initio band results as well as with experiment is found for the Fermi surface dimensions except for an absence of needles in Zn. For the d bands, it is found that in Zn they are localised above the conduction-band minimum, while in Cd they lie only partially above the conduction band.

http://iopscience.iop.org/article/10.1088/0953-8984/1/44/011/pdf

Electronic structure of Mg, Zn and Cd

A detailed study is presented on self-absorption of the K-M23, Mg-L23, and Al-L23 edges as well as new data on the anomalous Be-K edge which has already been presented by the author. The self-absorption mechanism is examined in some detail and it is concluded that under favourable circumstances, the absorption spectrum at the edge can be evaluated and its separation from the emission edge measured with a fair degree of accuracy. Broadening and other parameters have been determined for both emission and absorption and are discussed with reference to similar determinations by other workers.

Self-absorption studies of the soft X-ray emission and absorption edges of K, Mg, Al and Be

The x-ray photoemission spectra of the valence band region of Be, Na, Mg, and A1 have been measured and are analysed in terms of existing band structures. This allows an accurate determination of the band width of these metals and of the relative photoionisation cross sections (at ho)~ = 1487 eV) for the electrons of different angular momen

XPS investigation of simple metals: II. The Valence Band Spectra

The detailed energy band structures of hexagonal beryllium and magnesium have been computed by the composite-wave variational method in conjunction with the quantum defect method. From these energy band data, the density of states and Fermi surface of both these metals have been worked out and compared with the experimental and theoretical results of other workers. The results show a marked deviation of the energy bands of Be from the free electron behaviour, that for Mg being small. The Fermi surface of Be consists of a monster and two identical cigars, while that of Mg, following more or less the free electron nature, consists of several pieces in the form of a monster, cigars, lens, pockets and butterfly. These are found to agree favourably with experimental results.

https://iopscience.iop.org/article/10.1088/0305-4608/5/11/020/pdf

P Sinha

Papers

Energy band structure of beryllium and magnesium