Density functional theory is used to predict workfunctions, {psi}. For relaxed clean W(1 0 0), the local density approximation (LDA) agrees with experiment better than the newer generalized gradient approximation, probably due to the surface electron self-energy. The large Ba metallic radius indicates it covers W(1 0 0) at about 0.5 monolayer (ML). However, Ba{sup 2+}, O{sup 2-}, and metallic W all have similar radii. Thus 1 ML of BaO (one BaO unit for each two W atoms) produces minimum strain, indicating commensurate interfaces. BaO (1 ML) and Ba (1/2 ML) have the same {psi} to within 0.02 V, so at these coverages reduction or oxidation is not important. Due to greater chemical activity of ScO vs. highly ionic BaO, when mixing the latter with this suboxide of scandia, the overlayer always has BaO as the top layer and ScO as the second layer. The BaO/ScO bilayer has a rocksalt structure, suggesting high stability. In the series BaO/ScO/, BaO/YO/, and BaO/LaO/W(1 0 0), the latter has a remarkably low {psi} of 1.3 V (LDA), but 2 ML of rocksalt BaO also has {psi} at 1.3 V. We suggest BaO (1 ML) does not exist and that it is worthwhile to attempt the direct synthesis and study of BaO (2 ML) and BaO/LaO.
This document provides a user manual for the SGOPT software library. SGOPT is a C++ class library for nonlinear optimization. This library uses an object-oriented design that allows the software to be extended to a new problem domains. Furthermore, this library was designed to that the interface is straightforward while providing flexibility to allow new algorithms to be easily added to this library. The SGOPT library has been used by several software projects at Sandia, and it is integrated into the DAKOTA design and analysis toolkit. This report provides a high-level description of the optimization algorithms provided by SGOPT and describes the C++ class hierarchy in which they are implemented. Finally, installation instructions are included.
An effort is underway at Sandia National Laboratories to develop a library of algorithms to search for potential interactions between surfaces represented by analytic and discretized topological entities. This effort is also developing algorithms to determine forces due to these interactions for transient dynamics applications. This document describes the Application Programming Interface (API) for the ACME (Algorithms for Contact in a Multiphysics Environment) library.
The ability for scientific simulation software to detect and recover from errors and failures of supporting hardware and software layers is becoming more important due to the pressure to shift from large, specialized multi-million dollar ASCI computing platforms to smaller, less expensive interconnected machines consisting of off-the-shelf hardware. As evidenced by the CPlant{trademark} experiences, fault tolerance can be necessary even on such a homogeneous system and may also prove useful in the next generation of ASCI platforms. This report describes a research effort intended to study, implement, and test the feasibility of various fault tolerance mechanisms controlled at the simulation code level. Errors and failures would be detected by underlying software layers, communicated to the application through a convenient interface, and then handled by the simulation code itself. Targeted faults included corrupt communication messages, processor node dropouts, and unacceptable slowdown of service from processing nodes. Recovery techniques such as re-sending communication messages and dynamic reallocation of failing processor nodes were considered. However, most fault tolerance mechanisms rely on underlying software layers which were discovered to be lacking to such a degree that mechanisms at the application level could not be implemented. This research effort has been postponed and shifted to these supporting layers.