CAREER: Computer-Aided Design and Discovery of Novel Nanoporous Materials Through Ab Initio-Based Molecular Simulation

Purdue University, West Lafayette IN

Investigators

Abstract

Kendall K. Thomson Purdue University "CAREER: Computer-Aided Design and Discovery of Novel Nanoporous Materials Through Ab Initio-Based Molecular Simulation" The search for novel nanoporous materials is an exciting and active field of research. However, despite intensive investigation, discovery of novel nano-structured frameworks remains a mainly heuristic exercise. A key component in synthesizing many of these materials is the use of organic templating molecules that act as structure directing agents in the self-assembly of particular frameworks. What is needed is a means of (1) determining a priori which template molecules will synthesize which frameworks and (2) identifying what specific frameworks are possible that have not yet been discovered. The objective of this research is the development of a suite of computer tools to assist in the discovery and synthesis of novel nano-porous materials, and to initially apply these methods towards the discovery of novel titnaosilicate frameworks for gas separations and ion transport materials in fuel cell technology. The proposed program suite will combine two general algorithms: (1) framework-template matching, in which Monte-Carlo like moves are used to computationally "grow" template molecules within given frameworks, and (2) automated framework search, in which stochastic search methods combined with genetic algorithms are used to computationally search for feasible crystalline frameworks. In order for a molecular modeling approach to work, a proper accounting of interaction potential energy is required. For this a novel tight-binding prescription for silicate-based frameworks has been developed that is at least two orders of magnitude faster than ab initio dynamics, yet provides an accurate representation of oxide bonding properties. The method provides a fast and accurate means of incorporating full structural relaxation into the above algorithms, providing more realistic framework/template interactions and structural stability determination than previous methods. The method will initially be applied to the synthesis of titanosilicate frameworks of the ETS-4 and ETS-10 class, for which viable templates have not been identified. ETS-4 has thermal contraction properties that are currently exploited in gas separation technology. Suitable templates, if identified, could potentially alter the faulting behavior of these materials by directing the inter-growth of specific polytypes. This could result in materials with (1) novel contraction properties and (2) enhanced ion transport behavior, particularly applicable to fuel cell membrane technology. Further, novel titanosilicate frameworks with similar features to ETS-4 will be systematically sought. This proposed work will also address the challenge of bringing the molecular simulation knowledge base to the chemical engineering curriculum through the following activities: (1) development of theory and application based molecular simulation courses for the chemical engineering graduate curriculum, and (2) incorporation of a primarily application based, molecular simulation course in the undergraduate chemical engineering curriculum. The objective is to familiarize the chemical engineer with the utility and application of molecular simulation methods such they can communicate with experts in the field, identify situations where molecular simulation may be useful, and apply the techniques to problems in chemical engineering. In addition to molecular simulation competence the chemical engineer should be proficient in general modeling. The ability to competently analyze an engineering problem, formulate a working model, and extract useful information is key to effective problem solving capabilities, and suitable mathematical packages such as Mathematica can be useful teaching tools. Consequently, a web-based learning package will be developed that will emphasize the fundamentals of model building with workable Mathematica exercises and solutions that span the undergraduate curriculum. The goal is to integrate chemical engineering problems with modern mathematical computing tools that raise the technological standards of chemical engineering education. The impact of this development plan is expected to be broad and far reaching and will potentially effect every field where materials synthesis is required, including: catalysis, separations, sensor technology, fuel cell technology, nano-structured thermo-electronic materials, and nano-scale electric devices. The tight-binding prescription in itself represents a step forward in molecular simulation of zeolites and related ionic oxide materials, and will impact the zeolite/simulation community particularly in the areas of transport, adsorption, self-assembly and nucleation science, and zeolite isomorphic substitution chemistry. At the same time, by combining the discovery of new materials with the educational impact of incorporating simulation methods in the classroom, these proposed research and education activities offer an integrated program that serves the greater academic community through aggressive outreach and undergraduate enlightenment.