Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session A3: Frontiers in Computational Materials |
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Sponsoring Units: DCOMP TMS Chair: Giulia Galli, University of California, Davis Room: Morial Convention Center RO2 - RO3 |
Monday, March 10, 2008 8:00AM - 8:36AM |
A3.00001: Multi-Scale Modeling from First-Principles Invited Speaker: Electronic structure theory (the nature of the chemical bond) is the base and the finest scale for multi-scale modeling of the function of materials. Frequently it is assumed that details at this base do not matter when length and time scales approach meso- or macroscopic proportions (e.g. {$\mu$}m and minutes). In this talk I will show for various examples that details matter indeed. When accuracy is lacking at the base, there is little hope for predictive results at any level of modeling that follows. I will also emphasize the importance of reversible mapping and error control between the different levels of multi-scale modeling when moving up the chain of methods to successively increasing spatial and temporal dimensions. -- In this context I will also address the sometimes problematic accuracy of present day density functional theory methods and show how it can be determined and errors corrected. [Preview Abstract] |
Monday, March 10, 2008 8:36AM - 9:12AM |
A3.00002: Computational Approaches for Strongly Correlated Materials: an Electronic Structure Theory Perspective. Invited Speaker: Density functional theory known to work well for weakly correlated materials fails to attack real strongly correlated phenomena, and recent progress in understanding those using many-body model-hamiltonian-based dynamical mean-field theory has triggered developments of new approaches for computational material science in searching for alternatives to DFT. In this talk one of such new techniques, a spectral density functional theory, which considers total free energy as a functional of a local electronic Green function, will be discussed. Applications of the method to compute energetics, spectroscopy, lattice dynamics and exchange interactions of classes of materials such as heavy fermion and high temperature superconductors as well as actinide systems will be given. [Preview Abstract] |
Monday, March 10, 2008 9:12AM - 9:48AM |
A3.00003: First-principles studies of electrical transport in nanoscale molecular junctions Invited Speaker: Understanding the conductance of individual molecular junctions is a forefront topic in theoretical nanoscience. The development of a general, efficient atomistic approach for treating an open system out of equilibrium with good accuracy, and then using it to inform experiment, is a significant open challenge in the field. Here I will describe studies where first-principles techniques, based on density functional theory (DFT) and beyond, are used to investigate some of the fundamental issues associated with single-molecule transport measurements. After a brief summary of previous work, a DFT-based scattering-state approach is presented and applied to H$_2$ and amine-Au linked molecular junctions [1], two systems for which there exist reliable data [2]. Similar to most ab initio studies, we rely on a Landauer approach within DFT for junction conductance. Using this framework, which has proven relatively accurate for metallic point contacts, good agreement with experiment is obtained for the H$_2$ conductance. For amine-Au linked junctions, however, the computed conductance is significantly larger than that measured,although structural trends are reproduced by the calculations. To explore this further, we draw on GW calculations of a prototypical metal-molecule contact, benzene on graphite, where interfacial polarization effects are found to drastically modify frontier orbital energies [3]. A physically motivated model self-energy correction is developed from our GW calculations,applied to the amine case, and shown to quantitatively explain the discrepancy with experiment. The importance of many-electron corrections beyond DFT for accurately computing molecular conductance and understanding experiments is thoroughly discussed. [1] S. Y. Quek {\it et al.}, Nano Lett {\bf 7}, 3482 (2007); K. H. Khoo {\it et al.}, submitted (2007). [2] R. Smit {\it et al.}, Nature {\bf 419}, 906 (2002); L. Venkataraman {\it et al.}, Nature {\bf 442} ,904 (2006). [3] J. B. Neaton {\it et al.}, Phys. Rev. Lett. {\bf 97}, 216405 (2006). [Preview Abstract] |
Monday, March 10, 2008 9:48AM - 10:24AM |
A3.00004: First-Principles Thermodynamics and Kinetics of Advanced Hydrogen Storage Materials Invited Speaker: Hydrogen-fueled vehicles require a cost-effective, light-weight material that binds hydrogen strongly enough to be stable at ambient pressures and temperatures but weakly enough to liberate H2 with minimal heat input. Since none of the simple metal hydrides satisfy all the requirements for a practical H2 storage system, recent research efforts have turned to complex hydrides and advanced multicomponent material compositions. We will show that first-principles density-functional theory (DFT) calculations have become a valuable tool for understanding and predicting novel hydrogen storage materials. Recent studies in our group have used DFT calculations to (i) predict crystal structures of new solid-state hydrides, (ii) determine phase diagrams and thermodynamically favored reaction pathways in multinary hydrides, and (iii) study microscopic kinetics of diffusion, phase transformations, and hydrogen release. [Preview Abstract] |
Monday, March 10, 2008 10:24AM - 11:00AM |
A3.00005: Liquid Metal Embrittlement: new understanding for an old problem Invited Speaker: When liquid metals are brought into contact with other polycrystalline metals, deep liquid-filled grooves often form at the intersections of grain boundaries and the solid-liquid interface. In some systems, e.g., Al-Ga, Cu-Bi and Ni-Bi, the liquid film quickly penetrates deep into the solid along the grain boundaries and leads to brittle, intergranular fracture under the influence of modest stresses. This is a form of liquid metal embrittlement (LME).~ This phenomenon is ubiquitous in material processing and is particularly important in nuclear reactor scenarios in which liquid metals are used as coolants and as spallation targets. The penetration of a liquid phase along the grain boundary is a complex phenomenon, involving several different types of simultaneous processes. The tendency for and rate of LME are also sensitive to externally controllable factors such as temperature and applied stress. Because of the interplay between the underlying phenomena that occur in LME, it has been difficult to perform experiments that can be interpreted to understand which processes control LME and which are simply parasitic. We study LME by performing molecular dynamics simulations of an Al bicrystal in contact with liquid Ga and investigate how Ga penetrates along the grain boundaries during the early stages of the wetting process. We use the simulation results to propose a new mechanism for LME and compare it with general trends gleaned from a series of LME experimental studies. [Preview Abstract] |
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