Publications/2018

• Subramanian, Gopinath "Parallel Replica Dynamics of Bead‐Spring Elastomers at Low Strain Rates". Macromolecular Theory and Simulations. In Press. doi:10.1002/mats.201800010
  • A new application of the recently developed superbasin‐parallel replica (ParRep) method is presented. As a demonstration of this new application, mechanical properties of elastomeric networks of Lennard‐Jones polymer chains are calculated. In this application, superbasin boundaries are placed at locations in phase space corresponding to chain breakage. It is shown that placing superbasin boundaries at this natural location satisfies the prerequisites for using superbasin‐ParRep, and for the simulations conducted, leads to a near‐ideal scaling of wall clock time with the number of replicas, thereby demonstrating the potential for a drastic extension of simulation timescales for this class of systems.

• Sanjiv K. Jha, Michael Roth, Guido Todde, J. Paige Buchanan, Robert D. Moser, Manoj K. Shukla, and Gopinath Subramanian. "First-Principles Study of the Interactions between Graphene Oxide and Amine-Functionalized Carbon Nanotube" The Journal of Physical Chemistry C 2018 122 (2), 1288-1298 doi:10.1021/acs.jpcc.7b07502
  • We applied plane-wave density functional theory to study the effects of chemical functionalizations of graphene and carbon nanotube (CNT) on the properties of graphene–CNT complexes. The functionalizations of graphene and CNT were modeled by covalently attaching oxygen-containing groups and amines (NH2), respectively, to the surfaces of these carbon nanomaterials. Our results show that both dispersion energy and hydrogen bonding play crucial roles in the formation of complexes between graphene oxide (GO) and CNT–NH2. At a lesser degree of functionalization, the interaction energies between functionalized graphene and CNT were either unchanged or decreased, with respect to those without functionalization. Our study indicated that the gain or loss of interaction energy between graphene and CNT is a competition between two contributions: dispersion energy and hydrogen bonds. It was found that the heavy functionalization of graphene and CNT could be a promising route for enhancing the interaction energy between them. Specifically, the carboxyl-functionalized GO produced the greatest increase in the hydrogen bond strength relative to the dispersion energy loss. The influence of Stone–Wales defects in CNT on the computed interaction energies was also examined. The computed electron density difference maps revealed that the enhancement in the interaction energy is due to the formation of several hydrogen bonds between oxygen-containing groups of GO and NH2-groups of CNT. Our results show that Young’s moduli of carbon nanomaterials decrease with the increasing concentration of functional groups. The moduli of GO–CNT–NH2 complexes were found to be the averages of the moduli of their constituents.