The Center for Computational Materials Science performs basic and applied research on functional, structural, biological, and electronic material systems. Research includes the study of the fundamental physics and properties of materials and systems across wide ranges of length and time scales. The Center pioneers new methods for studying these systems including original computational and theoretical techniques for the modeling and development of materials of naval interest. The Center develops innovative scientific and engineering solutions for systems ranging from the atomic scale through the macroscopic, and from basic physics through the prototyping of devices for naval applications.

Current Research

Computational Methods

In addition to applying state of the art computational methods, the center for computational materials science develops methods that expand the range of applicability and increase the efficiency of simulations of materials with Naval relevance. These include tools for describing materials with chemical and structural complexity, for example accurate chemically-specific interatomic interactions, and methods for finite temperature and non-equilibrium properties.

Figure 1. CHx impurity species from decomposed trimethylaluminum precursors on an AlN surface during a kinetic Monte Carlo simulation. Yellow atoms are Al, blue are N, grey are C, and white are H." Electronic Materials

The advent of nitride semiconductor materials has enabled the new technology of solid-state lighting and established new capabilities in Navy-critical technologies such as power electronics. With wide band gaps over 3 eV and controllable electrical conductivity, the nitride semiconductor materials (including InN, GaN, and AlN) have made possible blue light-emitting diodes and high-power high-electron mobility transistors.

Realizing the full potential of the superior properties of these materials could allow for quarternary compounds with maximal band gap engineering and vertical device designs wit$ increased breakdown voltage. Achieving these advances will require ultralow impurity and defect incorporation and atomic-level control over film stoichiometry. This may be possible using growth techniques such as plasma-assisted atomic-layer deposition (PEALD) or homoepitaxial metal-organic chemical vapor deposition (MOCVD), but impurity incorporation (particu$ understanding process-property relationships have proven challenging.

Energy Storage and Generation

Many performance characteristics of energy storage systems, such as batteries or fuel cells can be traced back to materials properties of their individual constituents: anode, cathode and electrode. Quantities such as voltage, capacity and power are directly ca$ using first principles methologies such as Density Functional Theory (DFT). This allows for new materials to be evaluated or even designed at the computational level before expensive synthesis, characterization and testing ta$ in the lab. A primary concern of both the commercial and military sectors is the safety of Li ion batteries. The roots of how and why batteries fail can also often be found at the materials level. By calculating and underst$ phase stability, electronic structure and chemical stability of Li ion battery materials, the safety of the battery can be gauged and new materials and materials combinations to enhance safety and stability can be computationa$ developed.

Oxides

Our Center has a broad theoretical effort focusing on oxides. The systems include heterostructures, such as LaAlO3 films grown on SrTiO3, and bulk solid alloys. A multi-scale approach is generally used, building model hamiltonians from parameters computed with density functional theory.

Figure 1. Schematic structure of a semiconductor nanoplatelet. The platelet has a thickness of about 2 nanometers and lateral dimensions about ten times larger. The platelet material shown here is cadmium selenide in the zincblende crystal structure; cadmium atoms are shown as pink, selenium as yellow. The top and bottom surfaces are covered by a monolayer of acetate molecules, an organic ligand used to passivate the cadmium dangling bonds at the surface. For clarity, the acetate molecules on the thin side Semiconductor Nanostructures

Semiconductor nanostructures take a wide variety of physical forms and can be created from myriad different materials. One of the most active areas of this research focuses on semiconductor "nanoplatelets," the name given to nanostructures that are very thin and wide.

Nanoplatelets grown using colloidal synthesis methods are often atomically flat, as depicted in the figure. These quasi-two-dimensional sheets of semiconductor can exhibit efficient, spectrally pure fluorescence. This makes them uniquely well-suited for both fundamental investigations and future technological applications.

Figure: A schematic representation of the superconducting order parameter in different cases: a conventional, uniform, s-wave, such as in an 'old-fashioned' superconductor (for example aluminium)(a) (b) a d-wave, as is the case in copper oxides (c) a two-band s-wave with the same sign, as in MgB2 (d) an s± wave, as is thought to be the case in iron-based superconductors. In a and b, the two-dimensional Fermi surface is approximated by one circle. In c and d, the Fermi surface is approximated by a small circ Superconductors

We investigate existing unconventional superconductors (characterized by high-temperature and/or unusual pairing symmetries and mechanisms), with a goal to provide better understanding of their physical properties, mechanisms driving unusual superconductivity there, and outline for experimentalists directions for searching for new superconducting materials. As a starting point we usually, albeit not always, employ first-principle calculations of electronic structure of relevant materials.