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Gary G. Hoffman
Electronic Structure of Disordered Condensed Phase Materials: This work is aimed at developing an accurate and efficient means of determining the electronic structure of largescale systems that do not contain a great deal of periodicity. Glasses, grain boundaries, and materials with impurities are examples of systems to which such developments would apply. Attention has focused on the use of the optimized ThomasFermi theory. The theory has been shown to provide reasonably accurate electron distributions without the shortcomings of ThomasFermi theory, and the means of applying it to polyatomic systems has been devised. The extension to bulk systems is being developed. NonLocal Density Functional Theory without Gradients: Work in density functional theory has focused on the use of gradient corrections to the LDA. However, certain disadvantages exist with the associated functionals. A means of incorporating nonlocal behavior without using gradients is being developed and has shown promising results for the Hooke's atom system. Extensions are being worked on. Electronic Structure Calculations on some Interesting Systems: Electronic structure calculations using traditional techniques are being applied to various systems of interest. Particular cases are (i) the series of metalloporphyrins made from the firstrow transitions metals, paying attention to the effect of the central atom to the electron distribution about the periphery of the molecule and on the structure of the porphyrin ring, (ii) substituted olephins, noting the effect of electronwithdrawing groups on the nature of the double bond, (iii) the behavior of dinitrogen tetroxide when reacting with secondary amines, with hopes of elucidating the mechanism of nitration vs. nitrosation. Fermi Hypernetted Chain (FHNC) Theory Applied to Manyelectron Systems: The FHNC theory was originally developed for nuclear matter, but was found to be applicable to manyelectron systems as well. Calculations on the electron gas yielded results of comparable quality to QMC calculations. Extension of the theory to inhomogeneous systems is complicated, but has been worked out. Calculations have been applied to the embedded atom system. This work has led to some computational procedures for the general application of the method and has provided some interesting electron distributions for the systems that can be compared with results from other calculational methods. Additional work led to the derivation of the threebody equations. Application to the electron gas is planned. Stressstrain behavior of polymeric systems: A statistical theory of polymeric systems has been developed in which the molecular makeup of the material is quantitatively linked with its bulk level properties. Application has been made to rubberlike materials and the extension to viscoelastic materials has been carried out. Numerical simulations need to be performed to test the theory fully. Further, it is apparent the some of the approximations in the formalism need to be improved to obtain accurate predictive power. This work is now underway.
