Status & Challenges in Quantum Mechanics Based Modeling of Materials Behavior Emily A. Carter
Recently, a request has been put forth by the semiconductor and chemical industries to develop modeling techniques for accurate characterization and control of surface chemistry and materials phenomena over multiple time and length scales. An honest appraisal is given of the status and limitations of various methods spanning both length (electrons to continuum) and time (fs to hours) scales. In particular, while periodic density functional theory (DFT) has been anointed as the method of choice for a quantum mechanics description of surface and interfacial chemistry, it is best used as a qualitative indicator because its quantitative accuracy is still limited by its approximate description of electron exchange and correlation (XC). Photochemistry (which involves excited states and charge transfer), amorphous materials, strongly correlated systems (such as high Tc superconductors and Kondo materials), and molecular materials such as polymers (plastics, rubbers) are all poorly described within periodic DFT. These challenges are being worked on by a number of researchers, as outlined in the talk. One particular approach due to the author is presented, namely an embedded configuration interaction theory, which has been developed to enable an improved description of XC in a local region of condensed matter. This method has been used to accurately treat ground and excited states of adsorbates on metal surfaces and more recently to address the strongly correlated electronic effects arising in Kondo systems (magnetic impurities in non-magnetic host metals). Beyond electrons and atoms, one must examine ways to couple information from the atomic scale up the length scale ladder. Results will be presented that, e.g., couples atomic scale surface chemistry to millimeter scale mechanical stresses in order to realistically model stress corrosion cracking of steel via an informed continuum approach or simultaneously couples a very fast linear scaling DFT method (orbital-free DFT) to a finite element description of material deformation, in order to describe nano-indentation experiments. Lastly, open issues in multiscale modeling are laid out, with the ultimate goal of providing a seamless multiscale, multiphysics, adaptive description of materials behavior.
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