Use of molecular dynamics to uncover the operation of electrochemical nanodevices, design materials for shock energy absorption and metallic metamaterials with ultra-low stiffness

I will discuss our group’s recent work in extending molecular dynamics to incorporate the effect of degrees of freedom (DoFs) not captured explicitly by the particles. Examples of implicit DoFs are electrochemical potential or conduction electrons in all-atom MD and atoms internal to mesoparticles in coarse grain simulations. I will exemplify the use of the dynamics with implicit degrees of freedom (DID) method to various materials and devices of technological interest:

(1) Nanoscale resistance-switching cells that operate via the electrochemical formation and disruption of metallic filaments that bridge two electrodes are among the most promising devices for post-CMOS electronics. I will discuss the first atomistic simulations of their operation of conductive bridging cells using DID. The simulations predict the ultrafast switching observed experimentally and provide new insight into the atomistic mechanisms behind the development and dissolution of stable conducting filaments.

(2) We developed a coarse grain model to describe stress-induced chemical reactions and applied to guide the design of materials capable of attenuating shockwaves via endothermic, volume-reducing chemical reactions. The simulations show that such reactions can, indeed, weaken a propagating shock and enabled us to identify the key properties behind this effect. We found that the amount of volume contraction and the kinetics of the reactions, while the endothermicity of the reactions plays a minor role.

(3) We demonstrate ultra-low stiffness in fully dense metallic nanowires and laminates via the stabilization of a negative stiffness state using epitaxy. Key to predicting this unprecedented property is utilization of a martensitic alloy constrained to a mechanically unstable state by its coherent integration with a compatible, stable second component. Explicit large-scale molecular dynamics simulations confirm the low stiffness expected from the competing response of the two components and provide insight into the mechanisms behind ultra-low stiffness. These novel metamaterials exhibit Young’s moduli over one order of magnitude lower than either constituent, defying long-standing bounds of composite design.

Bio:

Alejandro Strachan is a Professor of Materials Engineering at Purdue University and the Deputy Director of the Purdue’s Center for Predictive Materials and Devices (c-PRIMED) and of NSF’s Network for Computational Nanotechnology. Before joining Purdue, he was a Staff Member in the Theoretical Division of Los Alamos National Laboratory and worked as a Postdoctoral Scholar and Scientist at Caltech. He received a Ph.D. in Physics from the University of Buenos Aires, Argentina, in 1999. Among other recognitions, Prof. Strachan was named a Purdue University Faculty Scholar (2012-2017), received the Early Career Faculty Fellow Award from TMS in 2009 and the Schuhmann Best Undergraduate Teacher Award from the School of Materials Engineering, Purdue University in 2007.

Prof. Strachan’s research focuses on the development of predictive atomistic and molecular simulation methodologies to describe materials from first principles, their application to problems of technological importance and quantification of associated uncertainties. Application areas of interest include: coupled electronic, chemical and thermo-mechanical processes in devices of interest for nanoelectronics and energy as well as polymers and their composites, molecular solids and active materials, including shape memory and high-energy density materials. He has published over 120 articles in the peer-reviewed scientific literature.