Periodic Slab LAPW Computations for Ferroelectric BaTiO3_3

Linearized augmented plane wave (LAPW) calculations are performed for periodic (001) and (111) slabs of BaTiO$_3$ to understand the effects of surfaces on ferroelectric BaTiO$_3$. The (111) slab is found to be much less stable than the (001) slab. The average surface energies are respectively 3700 erg/cm$^2$ and 1600 erg/cm$^2$. The depolarization field is sufficiently large in the ideal unrelaxated slab to completely inhibit the ferroelectric instability. No mid-gap surface states are evident, but there are surface states in the upper gap in the unrelaxed slab and at the top of the valence band. The dangling surface Ti bonds self-heal making the Ti-O surface very reactive and an excellent epitaxial substrate. The charge density on atoms only one unit cell away from the surface are almost identical to the bulk. Keywords: ferroelectric, surface, slab, electronic structure, depolarization, BaTiO$_3$, thin filmComment: LaTeX (RevTex),10 pages, 3 PS figures ( fig. 1 and fig. 3 are color), 1 table, J. Phys. Chem. Solids, Proceedings of Third Williamsburg Workshop on Fundamental Experiments in Ferroeletrics, T. Egami, edito

Investigating plate boundary zone deformation with geodetic GPS and modeling studies: A story of two ridges

The surface velocity field around plate boundaries and active faults contains information on a wide variety of processes and conditions, including the long-term fault slip rate, rheological properties of the crust and upper mantle and earthquake processes. Extracting this information requires not only high precision geodetic data, but also accurate models reflecting the critical properties of the crust and upper mantle, allowing us to relate the measurements (i.e., strain and strain rate) to the driving forces. The surface velocity field across two active plate boundaries was measured using high precision GPS geodesy and a combination of analytical elastic half-space models and numerical finite element modeling techniques were used to estimate lithospheric and fault parameters.The surface velocity field and modeling results for southern Iceland indicate that this divergent plate boundary has a complex pattern of strain accumulation due to its propagating nature. Strain accumulation is partitioned between the Western and Eastern Volcanic zones, whereby the spreading rate increases and decreases to the southwest, respectively.The surface velocity field and modeling results for the Central America, indicate that collision of the aseismic Cocos Ridge results in high degrees of coupling along the plate boundary. Strain is distributed in the upper plate across the forearc and back arc, resulting in terrane migration away from, and orogeny and subduction polarity reversal inboard of the rigid indenter