arXiv subjects

G. Brocks

Publications and source records attributed to G. Brocks.

22 records · Page 2Linked to original sources

arXiv2002

The difference between Si and Ge(001) surfaces in the initial stages of growth

The initial stages of growth of Ge and Si on the Ge(001) surface are studied and compared to growth on the Si(001) surface. Metastable rows of diluted ad-dimers exist on both surfaces as intermediate stages of epitaxial growth. Unexpectedly, for Ge(001) these rows are found exclusively in the <310> directions, whereas on Si(001) the preferred direction is <110>. This qualitative difference between Si and Ge surfaces reflects the subtle difference in the chemistry of these two elements, which has direct consequences for epitaxial growth on these surfaces.

cond-mat.mtrl-sci↗

arXiv2000

CaB_6: a new semiconducting material for spin electronics

Ferromagnetism was recently observed at unexpectedly high temperatures in La-doped CaB_6. The starting point of all theoretical proposals to explain this observation is a semimetallic electronic structure calculated for CaB_6 within the local density approximation. Here we report the results of parameter-free quasiparticle calculations of the single-particle excitation spectrum which show that CaB_6 is not a semimetal but a semiconductor with a band gap of 0.8 eV. Magnetism in La_xCa_{1-x}B_6 occurs just on the metallic side of a Mott transition in the La-induced impurity band.

cond-mat↗

arXiv2000

Ab-initio prediction of the electronic and optical excitations in polythiophene: isolated chains versus bulk polymer

We calculate the electronic and optical excitations of polythiophene using the GW approximation for the electronic self-energy, and include excitonic effects by solving the electron-hole Bethe-Salpeter equation. Two different situations are studied: excitations on isolated chains and excitations on chains in crystalline polythiophene. The dielectric tensor for the crystalline situation is obtained by modeling the polymer chains as polarizable line objects, with a long-wavelength polarizability tensor obtained from the ab-initio polarizability function of the isolated chain. With this model dielectric tensor we construct a screened interaction for the crystalline case, including both intra- and interchain screening. In the crystalline situation both the quasi-particle band gap and the exciton binding energies are drastically reduced in comparison with the isolated chain. However, the optical gap is hardly affected. We expect this result to be relevant for conjugated polymers in general.

cond-mat.mtrl-sci↗

arXiv1999

Ab-initio calculation of the electronic and optical excitations in polythiophene: effects of intra- and interchain screening

We present an calculation of the electronic and optical excitations of an isolated polythiophene chain as well as of bulk polythiophene. We use the GW approximation for the electronic self-energy and include excitonic effects by solving the electron-hole Bethe-Salpeter equation. The inclusion of interchain screening in the case of bulk polythiophene drastically reduces both the quasi-particle band gap and the exciton binding energies, but the optical gap is hardly affected. This finding is relevant for conjugated polymers in general.

cond-mat.mtrl-sci↗