Computational atomistic methods to design and investigate materials have seen tremendous growth in the last two decades because of a combination of factors, including the increased availability and low cost of fast computers, the refinement of atomistic methods, the growing availability of materials cyber-infrastructures, the shrinking of device dimensions, and the improved ability of experimentalists to study materials at the nanometer scale. It approaches well-established continuum level modeling (such as finite element analysis) and fluid dynamics at high length scales (100s-1000s nanometers), and overlaps with traditional physics and chemistry at small length scales (1-10 nanometers).
Research in the Sinnott group is focused on the application of computational methods at the electronic-structure and atomic scales to (1) examine the chemical modification of polymer and composite surfaces; (2) investigate the influence of grain boundaries, point defects, and heterogeneous interfaces on material properties; (3) design materials using a combination of computational methods, experiment, and data informatics within an interdisciplinary research team; and (4) determine the physical, chemical, optical and electrical properties of surfaces, nanostructures, and bulk materials.
Two-dimensional and nano-structured materials
Computational characterization of transition metal dichalcogenides (TMDs) and first principle study of interfacial structure of perovskite oxides thin film. As for TMDs, the objective of this work is to validate stability of doped monolayer structure and quantify the role of dopants on the structure-property relationships in 2D C-doped (Mo/W)S2 materials. As for perovskite oxides thin films, we study crystal structures of the thin films influenced by various substrates. The properties of thin films, including ferroelectricity, (anti-)ferromagnetism, and piezoelectric responses, are investigated.
Computational discovery of 2D nitrides guided by experiments. For example, recent investigations have shown the formation of 2D GaN in-between a SiC substrate and a graphene layer. Computational investigation aim to understand how the 2D GaN forms in this system and how the graphene layer aids in the formation of 2D GaN. Studies also aim to investigate other group III-V nitrides such as InN and AlN and their formation in the SiC-graphene system.
Metal nanoparticles for electrocatalysis
Investigation of metallic nanoparticles. Project is funded by the Department of Energy, Basic Energy Sciences. Carried out in collaboration with Prof. Ismaila Dabo. The focus of this project is investigating the structural and dynamical evolution of metallic nanoparticles and bimetallic nanoalloys under conditions consistent with their use in electrocatalytic applications, including oxidation effects on metal migration and the dissolution of these nanoparticles at solid-liquid interfaces. The focus is on Pt, which is an active electrocatalyst and is typically combined with other metals to maximize productivity while minimizing cost. A combination of computational methods is being applied to the problem, including density functional theory calculations, classical molecular dynamics simulations with reactive potentials, and cluster expansion modeling.
High-entropy materials
Computational investigation of high-entropy crystals within an inter-disciplinary research group. Most classical computational discovery paths are enthalpy stabilized, however instead, configurational disorder is employed as the thermodynamic driver to realize new crystalline solids. This work explores complex oxides with cation sublattices populated by many elements at random, known as high entropy oxides (HEOs). This research, which is part of the Materials Research Science and Engineering Center (MRSEC), explores the crystal chemistry rules of entropy-driven phases in search of transformational advances in materials properties by integrating synthesis, characterization, theoretical development, and computational modeling. Our current computational investigations are focused on the prototypical HEO, J14 [(Mg, Co, Cu, Ni, Zn)0.2O], as well as the leading HEO example for ionic conduction, F1 [Ce, La, Pr, Sm, Y)0.2O2-δ] where δ is some amount of oxygen vacancies.
Polymer-based Electrolytes for Electrochemical Energy Storage
Investigation of polymer-ceramic composite electrolytes. Recently, concern has risen due to use of flammable liquid organic electrolytes in Li-ion batteries, warranting the design of a replacement electrolyte material. As a part of the interdisciplinary Energy Frontier Research Center (EFRC) for Fast and Correlated Ion Transport in Polymer-based Electrolytes (FaCT), this multidisciplinary and multi-institutional project combines synthesis, theory, modeling, and characterization to build a predictive model for structure property relationships for ion transport in polymer-ceramic composite electrolytes to aid the design of new state-of-the-art battery electrolytes. We specifically contribute a combination of density functional theory calculations and classical molecular dynamics simulations.
Gas adsorption and separation in porous solid materials
Computational investigation of gas adsorption and separation in different porous solid absorbents. The Center for Understanding and Control of Acid Gas-Induced Evolution of Materials for Energy (UNCAGE-ME) was one of the Energy Frontier Research Centers (EFRCs) financed by the U.S. Department of Energy (DOE). The focus of the EFRC is to advance understanding of how acid gases interact with energy-related materials. UNCAGE-ME seeks to provide a fundamental understanding of acid gas interactions with solid materials through integrated studies of the interaction of key acid gases (CO2, NO2, NOx, SO2, H2S) with a broad range of materials. We combine the application of in situ molecular spectroscopic studies of both the surface functionalities and bulk structures of materials relevant to catalysis and separations under relevant environmental conditions with complimentary multiscale computational and theoretical modeling of acid gas interactions with solid matter.
Methodology development
A major area of emphasis is the development of inventive methods to enable the modeling of new material systems at the atomic level. Current efforts are focused on development and extension of the charge optimized many-body (COMB) potentials that allow for the modeling of heterogeneous systems that include materials with covalent, metallic, and ionic bonding within the same unit cell.
Previous work includes development of empirical potentials for molybdenum disulfide and reparameterized potential for hydrocarbons with oxygen. The formalism in these two empirical potentials is developed based on the reactive empirical bond order (REBO) potential.
All empirical potentials for the atomic-scale modeling of materials have been incorporated into the open-source large scale atomic-molecular massively parallel simulator (LAMMPS) software developed at Sandia National Laboratory to make them available to the scientific and engineering communities after rigorous testing, which are accessible from here.
