Current interests include studies of amorphous solid surfaces, bulk metallic glasses, CBRAM materials and their basic science and work on various related methods. We are collaborating with the group of Prof. Martin Fejer at Stanford on aspects of their LIGO project, and also with Profs. Stephen Elliott, Gábor Csányi and Dr. Volker Deringer at the University of Cambridge on DFT quality machine learning potentials and applications.
In the first set of images below, we take a random walk through our research with images associated with the structure, electronic, transport and vibrational properties of materials. Click on each for details.
Next: two generalized Wannier functions in silicon computed order-N by projection methods (crystal left, amorphous middle). The electron-phonon coupling is amplified for localized electrons — on the right, we see the LUMO level in a-Si with large phonon-driven charge fluctuations. See also here. Somewhat surprisingly, topological disorder in Si does not affect the spatial non-locality of quantum mechanics as measured by the decay of the single-particle density matrix. Also, localized Kohn-Sham eigenvalues and states are strongly modulated by thermal disorder.
Phonons in amorphous silica: note the non-locality and the mixing: E=500/cm. The message here is that local pictures of normal modes in glasses are grossly oversimplified. There is extensive mode mixing and non-locality, the details of which are very energy-dependent.
Finally, our approach to the Bragg problem for amorphous systems: Force Enhanced Atomic Refinement, here the example of amorphous silicon. The videos show the convergence of the radial distribution function (left) and topology (right) using FEAR (in the latter beige is experimentally realistic coordination). This is a general method that is far more efficient than melt quench methods and properly builds in a priori experimental information in the process of model construction while including ab initio chemical information in an unbiased way. See also this. The method is general and results are published for silver-doped chalcogenides, many forms of carbon, and bulk metallic glasses.