(220c) Quantum Mechanics Based Multiscale Reactive Simulations of Materials and Processes

Naserifar, S., California Institute of Technology
There is an economic and environmental imperative to develop new materials. Critical to the development and manufacturing of new generations of materials is the development of first-principles based multiscale multiparadigm methods and modeling software scalable from atoms to continuum, capable of efficiently predicting the dynamical behavior (reactive dynamics and kinetics) of the homogenous and heterogeneous materials. These methods are suitable for significantly improved performance of next generation materials. Recent dramatic developments in first-principles quantum mechanics (QM) methods has enabled accurate predictions for the properties of different systems. But the QM methods are limited to ~200 atoms and time scales of ~10 picoseconds (ps). In contrast, the developments of the new materials needed for dramatic improvements in the properties of materials under extreme conditions and electrochemical systems, for example, require spatial scales of 100 nm and beyond (>100 million atoms) and time scales of microseconds and beyond. Thus, there is an enormous gap between the scale of current QM methods and that of the real applications.

In my research I develop and validate the computation tools and software to fill this gap while simultaneously applying these methods to developing new generations of materials. Of my particular interest is the applications of these methods to electrochemical processes: batteries, fuel cells, and materials under extreme conditions: high energy density matters.

In this talk, I provide the details of development of these new advanced methods that provide near QM accuracy for reactive simulation of large systems. This provides the basis for in silico discovery of new combinations of materials that can subsequently be optimized.

In particular, I discuss the results of the simulations for water system because of its central role in life and importance in a lot of applications. We find quite excellent agreement with experimental data for solid and liquid phase of water: Tmelt=273.3K (exp=273.15K) and properties at 298K: ΔHvap=10.36 kcal/mol, density = 0.997 g/cc, entropy= 68.4 eu, dielectric constant=76.1, ln Ds (self-diffusion coef) =-10.08 compared to experimental values of 10.52, 0.997, 69.9, 78.4, and -11.24, respectively. We expect this model to remain accurate as a function of temperature and pressure. We have used this force field to study the properties of water at the surface including surface thickness, water orientation, hydrogen bond distribution, and vibrational frequencies which are experimentally hard to obtain. In addition, we have discovered for the first time the existence of six-coordinated water molecules at the areas close to the surface which are stable over 10 ps time intervals which could be responsible for some of the complicated water properties at the surface. I expect that we can use the above methods to extend it to ions, proteins, DNA, polymers, and inorganic systems for applications to biomolecular, pharma, electrocatalysis (fuel cells, water splitting) and batteries where interactions with explicit water molecules plays a significant role.