Session A10: Invited Session: Hard and Soft Materials Modeling, Simulations and Big Data

First-principles modeling of hard and soft matter

Electronic and atomistic processes are key to bio-inspired functional materials and nanocatalysts for energy applications. This talk will review recent simulation studies and discuss the challenges that first-principles quantum mechanical approaches face when addressing these issues.   

First Principles based methods and applications for realistic simulations on complex soft materials to develop new materials for energy, health, and environmental sustainability

For soft materials applications it is essential to obtain accurate descriptions of the weak (London dispersion, electrostatic) interactions between nonbond units, to include interactions with and stabilization by solvent, and to obtain accurate free energies and entropic changes during chemical, physical, and thermal processing. We will describe some of the advances being made in first principles based methods for treating soft materials with applications selected from new organic electrodes and electrolytes for batteries and fuel cells, forward osmosis for water cleanup, extended matter stable at ambient conditions, and drugs for modulating activation of GCPR membrane proteins,   

Nanoparticles in Complex Fluids, at Interfaces, in Polymers: Topology Matters

One versatile way to control the assembly and integration of nanoparticles is to tether organic molecules with specific functionalized groups to their surface. The tethers modify both inter particle interactions and their interaction with their surroundings, without disrupting the nanoparticles' unique properties. While it is often assumed that uniformly coating spherical nanoparticles with short organic ligands will lead to symmetric hybrids, using explicit-atom molecular dynamics simulations of model nanoparticles, we discovered that the hybrids exhibit a large variety of non-symmetric coatings, driving new pathways to control assemblies. These configurations of the coating stem from the high curvatures of small particles and comparable size tethers. In solution geometric factors dictate the symmetry of the hybrid and its stability, where the chain end-group coding and the solvent play only a secondary role. At water-vapor interface the anisotropic nanoparticle coatings seen in bulk solvents are enhanced. The coatings become significantly asymmetric and assume distinctive orientation with respect to the liquid interface. The asymmetry and degree of orientation depend strongly on the free volume provided by the geometry and the end group, as well as the solvent properties. At an interface asymmetric hybrids align with the surface to minimize free energy. These asymmetric coatings and oriented hybrids are expected to drive new self-assemblies symmetries in the bulk and at surfaces. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.   

Translocation of Small Interfering RNA and Cholesterol Molecules in Biomembranes

This presentation will focus on all-atom molecular dynamics (MD) simulation studies of (1) structural and mechanical barriers to translocation of small interfering RNA (siRNA) across a phospholipid bilayer, and (2) flip-flop dynamics of cholesterol (CHOL) molecules across a phospholipid bilayer. In the first case, we find that the siRNA induces a liquid-to-gel phase transformation. In the gel phase we find large compressive lateral stresses in the hydrocarbon chains of lipid molecules, which present a considerable barrier to siRNA passage across the bilayer. In the second case, we study spontaneous CHOL inter-leaflet transport (flip-flop), the effect of this process on mechanical stresses across the bilayer, and the role of CHOL in inducing molecular order in bilayer leaflets. The simulation was run for 15 microseconds and we found 24 CHOL flip-flop events over that duration. On average, a CHOL molecule migrates across the lipid bilayer in about 73 ns after a flip-flop event is triggered. We have calculated diffusion maps and determined free energy surfaces and flip-flop mechanisms for CHOL molecules.   

Multiscale modeling of nanostructures for electronic and energy-related applications

The optimization of materials properties for opto-electronic and energy-related applications is a crucial component in the design of new devices. To this end, multiscale modeling of nanostructures is essential in understanding and predicting materials properties ranging from optical response to the mechanical failure. We present a number of examples where multiscale modeling has yielded useful information concerning the optimal choices for nanostructured device elements. These include the excitation and charge transfer processes in hybrid photovoltaic devices, the tuning of optical and electrical properties of layered materials like graphene and transition-metal-dichalcogenides, and the mechanical response and deformation of silicon-based high-energy-density electrodes.