Research Samples

Spectrum of Exfoliable 1D van der Waals Molecular Wires and Their Electronic Properties

We reveal a spectrum of potentially exfoliable 1D wires and characterize their electronic properties. We characterize 1D van der Waals structures from several material families and find such low-dimensional components are potentially exfoliable, adding to the existing range of 2D stackable vdW materials and with potential applications such as interconnect replacements. DFT-MD (density functional theory-molecular dynamics simulations) on structures suggest the separated 1D chains are stable.

Developing a Novel DFT-Based Photoemission Model

We have developed a density functional theory (DFT) based method to model the photoemission process of photocathode materials with up to 5x less error than previously derived models. Coupled with the relatively low cost of performing DFT calculations, the general nature of our model may enable the possibility of rapidly screening through thousands of novel photocathode materials.

Uncovering atomistic mechanisms of crystallization using Machine Learning

Crystal growth is a challenging process to model quantitatively because of the notoriously complex atomic environments near solid-liquid interfaces. In order to make sense of such atomic environments we have introduced a novel data-driven approach to systematically detect, encode, and classify all atomic-scale mechanisms of crystallization. Machine learning and atomistic simulations were employed together to uncover the role of the liquid structure on the process of crystallization and derive a predictive kinetic model of crystal growth.

Machine Learning for Accelerated Discovery of promising Battery Materials

Using physics to guide our descriptions of known and unknown materials, we can screen tens of thousands of candidates to determine promising structures that satisfy requirements of future battery materials. We screen 12,000 candidates comprising all known lithium-containing inorganic crystalline solids and provide a list of 21 promising structures.

Revealing the Spectrum of Unknown Layered Materials with Super-human Predictive Abilities

It is a long-standing but as yet unrealized dream of computational material science to elucidate not just the properties of some materials but list all possible materials with a particular property. Here we accomplish this for the first time for two-dimensional layered materials by combining physics with machine learning.

Electrostatic gating drives structural phase transitions in monolayer materials

Two-dimensional transition metal dichalcogenides undergo structural semiconductor-to-semimetal phase transition under electrostatic gating of several volts.

Learning Kinetic Monte Carlo Models of Complex Chemistry from Molecular Dynamics

We use L1 regularization to reduce a large chemical reaction network observed from molecular dynamics simulations of shock compressed liquid methane, and find that CH4 decomposition can be modeled with less than 9% relative error using 11% of reactions.

Data mining to discover hundreds of new 2d and 1d materials.

We create a data mining algorithm that discovers hundresds of new 2d and 1d materials. Our algorithm searches through a database of roughly 70,000 materials that have been either synthesized or mined previously and determines which of the bulk structures exist in a layered or 1d wire form. This opens many opportunities for new 1d and 2d materials to be exfoliated or synthesized in the lab.

A defined Lifshitz model provides fast van der Waals computations for layered materials

We discover that a defined Lifshitz-based model can provide van der Waals (vdW) potentials to within 8-20% of advanced electronic structure calculations (ACFDT-RPA) while being orders of magnitude faster. Using this fast model, we study the vdW binding properties of 210 three-layered heterostructures and discover the potential for repulsive three-body vdW effects.

Atomistic simulation of shock-induced silica crystallization

Using the Multi-Scale Shock Technique for molecular dynamics simulation of millions of atoms, we discover that SiO2, a prototypical good glass former, can be transformed to a very bad glass former upon the application of high pressure by the shock compression of meteor impact.

Simulated coherent control of an isomerization reaction using THz electric field pulses

We have demonstrated simulated coherent control of a chemical isomerization, using strong THz electric field pulses to move the structure to a higher-energy state with only a few degrees of residual heating.

Strain Engineering in Monolayer Materials Using Patterned Adatom Adsorption

Our work shows that strains as large as 5% can be produced in monolayer materials using patterned adatom adsorption. Our results elucidate a method for strain engineering at the nanoscale in monolayer devices.

Deformations drive structural phase transitions in monolayer materials.

We discover that certain two-dimensional transition metal dichalcogenides undergo structural metal-to-insulator phase transitions under tension. Our calculations reveal that MoTe2 transforms at the smallest tensile strains: between 0.3 and 3% under uniaxial conditions.

Electromechanical Bending in Boron Nitride Bilayers

Our work reveals a unique and manifestly nanoscale curvature-electric field coupling in boron nitride bilayers. This discovery hints at the possibility of electrically controlling or sensing the curvature of a membrane that is only 0.3 nm thick.

Hydrogen and Fluorine coadsorption leads to piezoelectricity in graphene.

Motivated by a search for electromechanical coupling in monolayer materials, we have discovered that two types of piezoelectricity can be engineered into graphene when it is chemically modified with H and F.

Quantum corrections bring 40% lower pressure onset for methane dissociaton under shock compression.

We have developed a methodology for atomistic simulations of shock compressed materials that, for the first time, incorporates semi-classical quantum nuclear effects self-consistently. In our new method, the quantum nuclear effects are achieved with almost no additional computational expense.

Intrinsic Piezoelectricity in Two-Dimensional Materials

Our research has discovered that many of the widely studied two-dimensional monolayer crystals have excellent piezoelectric properties, making them ideally suited for applications in nanoscale technology.

Engineered Piezoelectricity in Graphene

Piezoelectric effects can be engineered into non-piezoelectric graphene through the selective surface adsorption of atoms.

Amino acid containing complexes may form in a shocked comet

Multi-scale simulations reveal that shock compression of comet ice (water + small organic molecules) may generate biologically-relevant molecules. In collaboration with LLNL.

A new ultrafast probe of phase transformations

Molecular dynamics simulations of shock waves in CdSe show that THz frequency electromagnetic radiation can be emitted and used as an ultrafast passive probe of the wurtzite to rocksalt phase transformation. The radiation contains information about the transformation pathway.