|My name is Bernard Wittmaack, and I’m a Ph.D. student in the department of materials science and engineering at the University of Virginia, working with Leonid Zhigilei. I completed the B.S. programs in both physics and chemistry at the University of Richmond, where I worked with Kelling Donald modeling chemical bonding with ab initio computational methods. Aside from research, I enjoy hiking, Shotokan karate, and practicing my cooking.|
My current research focuses on the computational modeling of carbon nanotube (CNT) materials such as forests and two dimensional films, using a coarse grained dynamic model that enables computationally efficient representation of systems consisting of tens of thousands of carbon nanotubes (CNTs). The model represents nanotubes as chains of stretchable cylindrical segments and accounts for the internal stretching, bending, and buckling of individual CNTs, as well as the inter-tube van der Waals interactions. A description of the energy exchange between the dynamic degrees of freedom of the mesoscopic model and the vibrational modes of CNTs that are not explicitly represented in the model is included through a "heat bath" approach designed and parameterized based on the results of atomistic simulations. Ultimately, my goal is to study the way CNT forests (see left figure) and films respond to particle impact, having implications in areas such as light weight armor and hazardous materials detectors. I am also interested in studying the thermal conductivity of various CNT forest structures, investigating the relative importance of the intrinsic heat conduction of CNTs and inter-tube heat exchange.
Much of the research is done with high performance computing (HPC) clusters (supercomputers) because the simulations I run need to keep track of millions of pieces of information, and many calculations are performed on each of these bits over thousands of time steps. Right now, our group has access to Titan, the world's fastest computer according to the TOP500 list. Located at Oak Ridge National Laboratory, Titan gains a lot of its power by utilizing the massive parallelization capability of GPUs.
To learn more about our research please visit the computational materials group website
(Left) Image of a CNT forest colored by bundle size
Crigger, C.; Wittmaack, B. K.; Tawfik, M.; Merino, G.; Donald, K. J. (2012) Plane and simple: planar tetracoordinate carbon centers in small molecules. Physical Chemistry Chemical Physics, 14, 14775-14783
Wittmaack, B. K.; Crigger, C.; Guarino, M.; Donald, K. J. (2011) Charge Saturation and Neutral Substitution in Halomethanes and their Group 14 Analogues. Journal of Physical Chemistry A. 115 (31), 8743-8753.
Donald, K. J.; Wittmaack, B. K.; and Crigger, C. (2010) Tuning σ -Holes: Charge Redistribution in the Heavy (Group 14) Analogues of Simple and Mixed Halomethanes Can Impose Strong Propensities for Halogen Bonding. Journal of Physical Chemistry A. 114 (26), 7213-7222.