Computationally Intensive Research Project
Absorption and Emission of Radiation in Materials
MSC News
Additional Information
L. Rene Corrales,1 Oliver A. Monti,1 B. G. Potter,1 Shawn M. Kathmann,2 Ram Devanathan,2 Renee M. Van Ginhoven,3 Steven H. Garofalini,4
1University of Arizona, 2Pacific Northwest National Laboratory, 3Sandia National Laboratory, 4Rutgers University
FY07 Allocation - 275,000
Abstract
Absorption of irradiation by a material can, for example, lead to changes of atomic and molecular configurations, and induce charged states in the form of defects or molecular rearrangements. Such responses modify the chemistry of the material that can invoke new reaction pathways; create channels for charge transfer; induce assembly or disassembly; and in general, form high-energy states of the system. The focus of the propose research is on the states of the system that arise from that event as opposed to the direct absorption or emission of a photon. The underlying scope of the project is to characterize and understand the mechanisms and factors that control energy absorption/desorption in the form of excited electronic states of molecular and atomic assemblies that make up heterogeneous environments.
Request for computational resources will be used to determine (as one concise example) the spectroscopic signatures that arise when a system undergoes a modification due to the absorption/desorption of photons. A goal is to comprehend in what form does the system "trap" energy, or in the case where energy is released what is the "source" of that energy. Changes in vibrational states, i.e. the appearance or disappearance of vibrational bands, can provide clues as to the state of the system after absorbing/desorbing a large amount of energy typically in the range of a quantum of light. Differences in vibrational signatures can then be compared with experiment to provide a molecular level characterization of structure associated with these excited energy states.
Different levels of ab initio theory along with different levels of basis sets provide different levels of accuracy for vibrational spectra, such as Raman and IR. However, underlying the introduction of a major conformation or geometric rearrangement are differences in spectral features. Ideally, the direct "response" of a molecule or assembly of atoms or molecules would be obtained directly from an ab initio calculation. That approach is practically forbidding, yet desirable. Theoretical strategies will be adopted and developed to provide a scope of likely structures that represent a response to the excitation for given classes of systems under investigation. The desire is to couple MS3 capabilities to build and modify structures using ECCE that then can be extensively studied using NWCHEM capabilities. Other codes to be used include GAMESS, GUESS, CPMD, and DLPOLY to carry out molecular ab initio and embedded-cluster calculations as well as ab initio and classical molecular dynamics simulations, respectively. Monte Carlo codes that take advantage of global arrays will also be used to investigate nucleation phenomenon in solutions.
