I did my grad work in Cornell’s Materials Science department, but my research was primarily computational physics. Most of the work revolved around the atomic structure prediction problem: if you put some atoms in a box, how do they like to arrange themselves? Knowing a material’s atomic structure is an important prerequisite to any theoretical prediction of it’s properties. Take, for example, carbon. It exists as both graphite (i.e. pencil lead) and diamond. Both materials are pure carbon – it’s just that the atoms are arranged differently. But clearly the two materials have much different properties.
Structure prediction can be framed as an optimization problem where we’re trying to minimize a thermodynamic quantity such as energy with respect to the atomic configuration. Unfortunately, accurate energy functions have many local minimums and are very expensive to sample. My work revolved around the use of evolutionary algorithms to solve this optimization problem as well as applications to a variety of technologically-interesting problems.
- Grand-canonical evolutionary algorithm for the prediction of two-dimensional materials. B. C. Revard, W. W. Tipton, A. Yesypenko, and R. G. Hennig. Phys. Rev. B 93, 054117 (2016). (link)
- ReaxFF Molecular Dynamics Simulations on Lithiated Sulfur Cathode Materials. A. Ostadhossein, O. Borodin, A. T. Yeates, W. W. Tipton, R. G. Hennig, M. D. Mahbubul Islam, and A. van Duin. Phys. Chem. Chem. Phys. 17, 3383 (2015). (link)
- Importance of high angular momentum channels in pseudopotentials for quantum Monte Carlo. W. W. Tipton, N. D. Drummond, and R. G. Hennig. Phys. Rev. B 90, 125110 (2014). (link)
- Ab-initio prediction of the Li5Ge2 Zintl compound. W. W. Tipton, C. A. Mathulis, and R. G. Hennig. Comp. Mater. Sci. 93, 133 (2014).(link)
- Structure and Stability Prediction of Compounds with Evolutionary Algorithms. B. C. Revard, W. W. Tipton, and R. G. Hennig. Topics in Current Chemistry 345, 181 (2014) (link)
- A grand canonical genetic algorithm for the prediction of multi-component phase diagrams and testing of empirical potentials. W. W. Tipton and R. G. Hennig. J. Phys.: Cond. Matter 25, 495401 (2013). (link}
- Structures, Phase Stabilities, and Electrical Potentials of Li-Si Battery Anode Materials. W. W. Tipton, C. R. Bealing, K. Mathew, R. G. Hennig. Phys. Rev. B 87, 184114 (2013). (link)
- Ab initio based empirical potential used to study the mechanical properties of molybdenum. H. Park, M. R. Fellinger, T. J. Lenosky, W. W. Tipton, D. R. Trinkle, S. P. Rudin, C. Woodward, J. W. Wilkins, and R. G. Hennig. Phys. Rev. B 85, 214121 (2012). (link)
- Computationally-Driven Experimental Discovery of the CeIr4 In Compound. D. J. Fredeman, P. H. Tobash, M. A. Torrez, J. D. Thompson, E. D. Bauer, F. Ronning, W. Tipton, S. P. Rudin, and R. G. Hennig. Phys. Rev. B 83, 224102 (2011). (link)
- Pressure-induced structure transitions in Eu metal to 92 GPa. W. Bi, Y. Meng, R. S. Kumar, A. L. Cornelius, W. W. Tipton, R. G. Hennig, Y. Zhang, C. Chen, and J. S. Schilling. Phys. Rev. B 83, 104106 (2011). (link)
- Random Search Methods. W. W. Tipton and R. G. Hennig. In Modern Methods of Crystal Structure Prediction (ed. A. R. Oganov), Wiley-VCH, Weinheim, Germany (2010). (link)
- First Blind Test of Inorganic Crystal Structure Prediction Methods. A. R. Oganov, J. C. Schon, M. Jansen, S. M. Woodley, W. W. Tipton, R. G. Hennig. In Modern Methods of Crystal Structure Prediction (ed. A. R. Oganov), Wiley-VCH, Weinheim, Germany (2010). (link)