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Complex oxides are among the most abundant minerals on earth. While the mixture of metal elements and oxygen ions is common to all complex oxides, it is the interactions of these elements which determine the material's response to its environment. Probing the bonding interactions within these materials is fundamental to the design of new materials. This thesis uses both ab initio and classical modeling to examine the bulk and interfacial properties of complex oxides. Ab initio density functional theory (DFT) calculations are used to study how composition and ordering of Ti and Zr in PbZr1-xTixO3 (PZT) affect the displacement of ions within the PZT unit cell. The investigation of a variety of compositions and arrangements of these cations made it possible to distinguish the physical and chemical properties which are dependent on local environment from those intrinsic to the material. However, a comparison of the calculated pair distribution functions (PDF) with those obtained from neutron scattering experiments suggested that the DFT supercells used were too small to account for the long range disorder in the real material. To correct this, a classical model which reproduces the short range interactions in DFT calculations and is capable of simulating larger unit cells was constructed. These results indicated that the local interactions governing the DFT calculations were also key in defining the macroscopic structure of PZT. Guided by this theory, the model was reparameterized to study the temperature dependent phase transition of PbTiO3 (PT). These simulations demonstrated that the principles inherent in the classical model are valid for investigating dynamical properties of various perovskite oxides. The final project presented in this thesis explores the mechanism of charge transfer at a metal-oxide interface and its influence on the metal surface properties. Here it is shown that a mixture of ionic and covalent bonding at this interface affects the charge distri

We have computationally designed new materials for use in Naval SOund NAvigation Ranging (SONAR). Our quantum-mechanical studies show that these lead-free, non-toxic oxides will be high-performance piezoelectrics with promise for use in Naval SONAR and communications applications. To enable this research, we also present techniques for greatly accelerated modeling of oxide materials. We show that a simple atomistic model accurately reproduces our quantum-mechanical results yet is thousands of times faster. We also report successful porting and performance tuning of our computer codes to the CRAY XI, resulting in a great speed-up over previous architectures., Presented at the DoD High Performance Computing Modernization Program (HPCMP) Users Group Conference (UGC), held in Williamsburg, Virginia on 7-11 June 2004. Sponsored in part by National Science Foundation (NSF) grant no. DMR00-79909. The original document contains color images. All DTIC reproductions will be in black and white. This article is from ADA492363 Proceedings of the HPCMP Users Group Conference 2004.