Valence Charge Density Distribution Research Articles

The surface electronic structure and scanning tunneling microscopy of WTe2

We have investigated the surface electronic structure of the van der Waals surfaces of tungsten ditelluride (WTe2) with first principles calculations of the spatial distribution of the surface valence charge densities and compared the results to images obtained with scanning tunneling microscopy (STM). The energy-dependent calculations show that the valence charge density distributions above the Te surface could be derived from the surface Te layer, as we previously calculated, but the charge density distribution has a distortion that makes it appear to have a symmetry close to the paired, zig-zag and buckled rows of the W layer. These results dramatically illustrate that the surface valence charge density distribution does not necessarily follow the surface atomic positions even on an ideal, unreconstructed surface. An alternative interpretation of the STM images of this surface will be proposed in light of these new findings in the surface electronic structure.

Comparison of charge density distribution and electronic bonding in α-SiO 2 and β-Si 3N 4

The electronic structures of α-SiO 2 and β-Si 3N 4 are studied by the first-principles self-consistent orthogonalized LCAO method. The calculations were done with three different sets of basis functions ranging from minimal to full basis. The valence charge density distribution shows little variation with the basis functions but the gap value decreases as the basis is enlarged. The nonspherical charge distribution on the Si atoms is restricted to a smaller region (than N or O) with an ionic radius of about 0.4 Å and there is no charge build-up along the Si—O or Si—N bonds, indicationg that electronic bonding is more ionic than covalent in both crystals. In β-Si 3N 4, the charge distribution appears to be confined to the Si 3N 4 molecular unit as a whole.