We have determined the atomic structure and formation energies of small, compact self-interstitial clusters ͑I n , n ഛ 10͒ in Si using a combination of Metropolis Monte Carlo, tight binding molecular dynamics, and density functional theory calculations. We present predicted local-minimum configurations for compact selfinterstitial clusters with n = 5 -10, together with well-defined smaller clusters ͑n ഛ 4͒ for comparison. The cluster formation energies per interstitial exhibit strong minima at n = 4 and 8.

Simulating lignocellulose-derived pyrolysis oil, the effects of carbohydrate derivatives on the hydrodeoxygenation of lignin-derived phenolic compounds, guaiacol in this study, were observed using supported ruthenium catalysts. Among several carbohydrate derivatives which possibly exist in the pyrolysis oil, the addition of furfural and 5-hydroxy­methylfurfural (5-HMF) significantly decreased the conversion of guaiacol, with density functional theory (DFT) calculations indicating that guaiacol competes with furfural and 5-HMF to adsorb onto the ruthenium nanoparticle surface, thus suppressing the hydrogenation of guaiacol.

We examined mechanisms underlying Si nanocrystal formation in Si-rich SiO 2 using a combination of quantum mechanical and Monte Carlo ͑MC͒ simulations. We find that this process is mainly driven by suboxide penalty arising from incomplete O coordination, with a minor contribution of strain, and it is primarily controlled by O diffusion rather than excess Si diffusion and agglomeration. The overall behavior of Si cluster growth from our MC simulations based on these fundamental findings agrees well with experiments.

Catalysts that are highly selective and active for H2 production from HCOOH decomposition are indispensable to realize HCOOH-based hydrogen storage and distribution. In this study, we identify two effective routes to promoting the Pd catalyst for selective H2 production from HCOOH by investigating the effects of early transition metals (Sc, Ti, V, and Cr) incorporated into the Pd core using density functional theory calculations. First, the asymmetric modification of the Pd surface electronic structure (d z 2 vs d yz + d zx ) can be an effective route to accelerating the H2 production rate. Significant charge transfer from the subsurface Sc atom to the surface Pd atom and subsequent extremely low level of d band occupancy (<0.1) around the Sc atoms are identified as a key factor in deriving the asymmetric modification of the Pd surface electronic structure. Second, in-plane lattice contraction of the Pd surface can be an effective route to suppressing the CO production. Compressive strain of the Pd surface is maximized as a result of alloying with V and induces subsequent changes in adsorption site preference of the key intermediates for the CO production path, resulting in a significant increase in the activation energy barrier for the CO production path. The unraveled atomic-scale factors underlying the promotion of the Pd surface catalytic properties provide useful insights into the efforts to overcome limitations of current catalyst technologies in making the HCOOH-based H2 storage and distribution economically feasible.

Using a density functional theory approach, we examine the dielectric function (ε(ω)) optical spectra and electronic structure of various silicon nanowire (SiNW) orientations (<100>, <110>, <111>, and <112>) with amorphous oxide sheaths (-a-SiOx) and compare the results against H-terminated reference SiNWs. We extend the same methods to investigate the effects of surface passivation on <111> SiNW properties using functional group termination (-H, -OH, and -F) and three different thicknesses of oxide sheath passivation. Oxide layer growth is evidenced in the spectra by concomitant appearance of tail oxide character with signatures of increased Si disorder. Suboxide contributions and increased Si disorder from oxidation average out the band structure dispersion observed in the reference SiNWs. Furthermore, we plot average Seraphin coefficients for <111> passivations that clearly distinguish functional group termination from surface oxidation and discuss the suboxide and disorder contributions on the characteristic intersection of these coefficients. The substantial difference in properties observed between <111>-OH and <111>-a-SiOx SiNWs emphasizes the importance of using realistic oxidation models to improve understanding of SiNW properties.