Since their modern debut in 2004, 2-dimensional (2D) materials continue to exhibit scientific and industrial promise, providing a broad materials platform for scientific investigation, and development of nano-and atomic-scale devices. A significant focus of the last decade's research in this field has been 2D semiconductors, whose electronic properties can be tuned through manipulation of dimensionality, substrate engineering, strain, and doping. 1-8 2D semiconductors such as molybdenum disulfide (MoS2) and tungsten diselenide (WSe2) have dominated recent interest for potential integration in electronic technologies, due to their intrinsic and tunable properties, atomic-scale thicknesses, and relative ease of stacking to create new and custom structures. However, to go "beyond the bench", advances in large-scale, 2D layer synthesis and engineering must lead to "exfoliation-quality" 2D layers at the wafer scale. This roadmap aims to address this grand challenge by identifying key technology drivers where 2D layers can have an impact, and to discuss synthesis and layer engineering for the realization of electronic-grade, 2D materials. We focus on three fundamental areas of research that must be heavily pursued in both experiment and computation to achieve high-quality materials for electronic and optoelectronic applications. The document is organized as follows:

Using a reactive force field ͑ReaxFF͒, we investigated the structural, energetic, and adhesion properties, of both solid and liquid Al/␣-Al 2 O 3 interfaces. The ReaxFF was developed solely with ab initio calculations on various phases of Al and Al 2 O 3 and Al-O-H clusters. Our computed lattice constants, elastic constants, surface energies, and calculated work of separation for the solid-solid interface agree well with earlier first-principles calculations and experiments. For the liquid-solid system, we also investigated the nonwetting-wetting transition of liquid Al on ␣-Al 2 O 3 (0001). Our results revealed that the evaporation of Al atoms and diffusion of O atoms in ␣-Al 2 O 3 lead to the wetting of liquid Al on the oxide surface. The driving force for this process is a decrease in interfacial energy. The nonwetting-wetting transition was found to lie in the 1000-1100 K range, which is in good agreement with sessile drop experiments.

Vanadyl oxide (VO) sites are thought to play a role in a number of industrially important catalysts for activating saturated alkanes, but in no system is the mechanism for the activation, product formation, and reoxidation steps established. In this paper, we use quantum mechanical methods (B3LYP flavor of density functional theory) to examine the detailed mechanism for propane reacting with a V4O10 cluster to model the catalytic oxidative dehydrogenation (ODH) of propane on the V2O5(001) surface. We here report the mechanism of the complete catalytic cycle, including the regeneration of the reduced catalyst using gaseous O2. The rate-determining step is hydrogen abstraction by the vanadyl (VO) group (in agreement with experiment) to form an iso-propyl radical that binds to an adjacent V−O−V site. Subsequently, this bound iso-propyl forms propene product by β-hydride elimination to form bound H2O. We find that this H2O (bound to a VIII site) is too stable to desorb unimolecularly. Instead, the desorption is induced by binding of gaseous O2 to the VIII site, which dramatically decreases the coordination energy of H2O from 37.8 to 12.9 kcal/mol. Further rearrangement of the O2 molecule leads to formation of a cyclic VO2 peroxide, which activates the C−H bond of a second propane to form a second propene (with a lower reaction barrier). Desorption of this propene regenerates the original V4O10 cluster. We find that all reactions involve the single vanadyl oxygen (VO), with the bridging oxygens (V−O−V) serving to stabilize the iso-propyl radical intermediate. We refer to this mechanism as the single-site vanadyl activation, functionalization, and reoxidation mechanism (SS-VAFR). This SS-VAFR mechanism should be applicable to propane ODH on the supported vanadium oxide catalysts where only monovanadate (VO4) species are present.

The successful discovery and isolation of graphene in 2004, and the subsequent synthesis of layered semiconductors and heterostructures beyond graphene have led to the exploding field of two-dimensional (2D) materials that explore their growth, new atomic-scale physics, and potential device applications. This review aims to provide an overview of theoretical, computational, and machine learning methods and tools at multiple length and time scales, and discuss how they can be utilized to assist/guide the design and synthesis of 2D materials beyond graphene. We focus on three methods at different length and time scales as follows: (i) nanoscale atomistic simulations including density functional theory (DFT) calculations and molecular dynamics simulations employing empirical and reactive interatomic potentials; (ii) mesoscale methods such as phase-field method; and (iii) macroscale continuum approaches by coupling thermal and chemical transport equations. We discuss how machine learning can be combined with computation and experiments to understand the correlations between structures and properties of 2D materials, and to guide the discovery of new 2D materials. We will also provide an outlook for the applications of computational approaches to 2D materials synthesis and growth in general.npj Computational Materials (2020) 6:22 ; https://doi.

To investigate the reaction kinetics of hydrogen combustion at high-pressure and high-temperature conditions, we constructed a ReaxFF training set to include reaction energies and transition states relevant to hydrogen combustion and optimized the ReaxFF force field parameters against training data obtained from quantum mechanical calculations and experimental values. The optimized ReaxFF potential functions were used to run NVT MD (i.e., molecular dynamics simulation with fixed number of atoms, volume, and temperature) simulations for various H(2)/O(2) mixtures. We observed that the hydroperoxyl (HO(2)) radical plays a key role in the reaction kinetics at our input conditions (T ≥ 3000 K, P > 400 atm). The reaction mechanism observed is in good agreement with predictions of existing continuum-scale kinetic models for hydrogen combustion, and a transition of reaction mechanism is observed as we move from high pressure, low temperature to low pressure, high temperature. Since ReaxFF derives its parameters from quantum mechanical data and can simulate reaction pathways without any preconditioning, we believe that atomistic simulations through ReaxFF could be a useful tool in enhancing existing continuum-scale kinetic models for prediction of hydrogen combustion kinetics at high-pressure and high-temperature conditions, which otherwise is difficult to attain through experiments.