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Multiscale Virtual Design and Testing of Materials Print E-mail
Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio   
Aug 01 2007
Page 2 of 3
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  • The first method for combining continuum and atomistic descriptions of defects within one conceptual framework. The framework is a model that combines power of the aforementioned discrete-dislocation model with the atomistic resolution of molecular dynamics.
  • The first model to couple quantummechanical and atomistic submodels for metals. In this model, either standard density-functional theory (DFT) or orbital-free density-functional theory (OF-DFT) is used to embed quantum- mechanical calculations within an atomistic computational submodel that employs semi-empirical atomistic potentials.
  • Extension of a static, zero-temperature quasi-continuum model to nonzero finite temperature. The extension was made by considering a formal “coarse graining” of the microscopic partition function of a classical material at finite temperature, then generating an approximate effective coarsegrained potential by making a selfconsistent quasi- harmonic approximation for the atoms that were eliminated through the coarse graining process.
  • The first quantum/continuum coupling method. This method provides for utilization of first-principles OFDFT calculations in a “local” quasicontinuum model. The energy of strained unit cells of a material is used to compute the deformation of the material in continuum domains that are treated by use of finite elements.
  • The first quantum-mechanical determination of decohesion with and without embrittlement by impurities. DFT was used to predict the fundamental cohesive behaviors of metals with and without hydrogen and oxygen atoms as impurities along separating surfaces. The appropriate thermodynamic potential (the so-called grand force potential) was developed for converting the results of computations of decohesion at fixed impurity concentration to those of decohesion at fixed chemical potential. It was shown that the cohesive strength of aluminum drops precipitously, from about 12 GPa to 4 GPa in hydrogen and to between 1 and 2 GPa in oxygen when the chemical potential exceeds a critical value.

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