The electron density of beryllium derived from 0·12 Å γ-ray diffraction data

Abstract

A large set of structure factors for beryllium has been measured with a 0.12/~ y-ray diffractometer. The present data are in good agreement with other recent X-ray and y-ray diffraction measurements. Extinction was significant though not very strong. Deformation density maps confirm that the bonding goes through the tetrahedral holes of the hexagonal close-packed structure. Comparisons with band-structure calculations indicate that the local-density approximation to the density functional theory is valid for beryllium. The quality of the data, combined with the earlier experimental results, is sufficient to demonstrate that the structure factors are sensitive to the valence electron hybridization even at high momentum transfer [(sin 0)/A > 0.75 A-I]. Core electron deformation is a much smaller effect.

Experimental and Theoretical Charge Density Studies at Subatomic Resolution

“…Hence, κ core and κ valence denote expansion/contraction parameters of the respective shells. In this respect, our model goes beyond earlier attempts to merely adjust the core contraction/expansion of light elements (e.g., Be) by high-order refinements of a single κ-parameter for both core and valence shells . Indeed, the necessity of a variable core population has been addressed by a number of pioneering studies, − and we will show later that for second row and heavier elements even individual P j ,c and κ core parameters need to be adjusted to fit the expansion/contraction and deformation of each shell of bonded atoms in molecules and solids.…”

“…We will also comment on earlier and alternative concepts to refine core density distributions. 3,40,2,49,39 3.2. Experimental Core j Refinements: A Combined Rietveld/Multipolar Approach.…”

“…In the next section, we will discuss whether core contraction/expansion effects are relevant for experimental studies and which experimental resolution and data precision are needed to identify these tiny effects. We will also comment on earlier and alternative concepts to refine core density distributions. ,,,, …”