Alternative approach to computing transport coefficients: application to conductivity and Hall coefficient of hydrogenated amorphous silicon

We introduce a theoretical framework for computing transport coefficients for complex materials. As a first example, we resolve long-standing inconsistencies between experiment and theory pertaining to the conductivity and Hall mobility for amorphous silicon and show that the Hall sign anomaly is a consequence of localized states. Next, we compute the AC conductivity of amorphous polyanaline. The formalism is applicable to complex materials involving defects and band-tail states originating from static topological disorder and extended states. The method may be readily integrated with current \textit{ab initio} methods.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let

Christian Steven (1781–1863) at the Lower Volga

Christian Steven made several excursions to the Caucasus, Crimea and the southern provinces of Russia. He visited occasionally also Lower Volga area and did botanical collections, jointly with Marschall von Bieberstein in 1800. In this article, we present Stevens activity here. He collected plant specimens in Lower Volga area in 1800, 1806, 1811 and 1816. Based on specimens collected here, and in some cases additionally also elsewhere, Steven described Adonis volgensis (1817), Ceratocephala incurva (1848), C. leiocarpa (1848), C. reflexa (1848) and Centaurea gerberi (Steven 1856). Further, Allium sabulosum (Steven ex Bunge 1838) and Delphinium cuneatum (Steven ex DC. 1818) were described based on material Steven collected in this region