Computational atomistic methods to design and investigate materials have been 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 increasing 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 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 doped 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.
Thermodynamic stability and theoretical performance of alloyed MXenes as Lithium-Ion Battery electrodes. MXenes, a group of layered transition metal carbides and nitrides, show promise for applications in electrochemical energy storage devices. There is a large compositional space for these materials: M being an early transition metal, X being carbon or nitrogen with varying terminating groups, T, that depend on sythesis conditions. Some of these materials such as Ti3C2, have been tested as high capacity Lithium-Ion Battery electrodes. A wealth of recent studies, both theoretical and experimental, show that alloy MXenes can be sythesized as well. In our group, we use modeling techinques to predict the theoretical capacity of alloy MXenes, their stability, and open circuit potentials.
Gas adsorption and separation in porous solid materials
Computational investigation of gas adsorption and separation in different porous solid absorbents. For instance, carbide-derived carbon (CDC) is a new disordered porous carbon structure, and incompleted etching of carbide precursors produces residual metals in CDCs that may enhance acid gas uptake. Ordered porous structures such as porous aromatic framework (PAF) and metal organic framework (MOF) may also be further functionalized by organic/inorganic groups for gas separation. Other studies that related to CDC project are the Al-C COMB potential development and 2D materials such as graphene, MXene and hybrid systems. Methods applied in my studies include first-principle calculations, molecular dynamics simulations and Monte Carlo simulations.
“Computational investigation on CO2 adsorption in titanium carbide-derived carbons with residual titanium”, D. Zhang, M. R. Dutzer, T. Liang, A. F. Fonseca, Y. Wu, K. S. Walton, D. S. Sholl, A. H. Farmahini, S. K. Bhatia, S. B. Sinnott, Carbon 111, 741-751, (2017). DOI: https://doi.org/10.1016/j.carbon.2016.10.037
Mechanical properties of condensed matters
The tribological properties of glass. Such calculations involve calculating the coefficient of friction in different environments such as different relative humidity levels. Also considered are different cations involved in the glass composition such as sodium or calcium.
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.