Energy Landscape Investigations of Chemical Matter and Structure Prediction of Binary Inorganic Solids

Recent developments in experimental solid state chemistry have offered us new possibilities in controlling synthesis routes, especially by varying the pressure and temperature. Similarly, the development of new theoretical methods and tools makes it worthwhile to reinvestigate apparently well-known systems. In this thesis several binary systems, in particular PbS and ZnO, have been investigated using several different theoretical methods. Since lead sulfide is an important semiconductor, it is of great interest to identify possible (meta)stable modifications, both at standard and elevated pressures. To predict such structures, global optimizations on the energy landscape of PbS were performed for several pressures, using simulated annealing followed by local optimizations of the candidates found. In order to be able to take the effect of the non-bonding valence electrons of Pb into account, ab initio energies were employed for both the global and local optimization. Besides the experimentally known modifications (NaCl structure type at standard pressure and the CsCl structure type at high pressure), several additional promising structures, which might be accessible synthetically, were found; exhibiting e.g. the TlI type (Cmcm), the FeB type (Pnma), and the α-GeTe-type (R3m). E(V ) curves and H(p) curves were calculated and analyzed, and further properties of the new modifications were investigated by performing band structure and phonon calculations. In order to gain new insights in the ZnO system, we have performed global explorations of the energy landscape using simulated annealing with an empirical potential, both at standard and elevated pressure (up to 100 GPa). Besides the well-known structure types (wurtzite, sphalerite and rock-salt), many new interesting modifications were found in different regions of the energy landscape, e.g. the âĂIJ5-5âĂİ type, the GeP, the NiAs type, and the β-BeO type. Furthermore, we observed many distorted varia-