Frank W. Averill

Embedded-cluster self-consistent partial-wave method: Extending the spatial scale of electronic structure calculations

An efficient approach to extending the spatial scale of electronic structure calculations is described in this work. The method is formulated as a combination of the interacting fragments concept of Harris [J. Harris, Phys. Rev. B 31, 1770 (1985)] and the D&C method of Yang [W. Yang, Phys. Rev. Lett. 66, 1438 (1991)], which recognizes the intrinsic locality of electron bonding and is devised to optimize the total electron charge density within an approximate representation of partitioned components. Beginning with a brief review of D&C concepts, we report results from this new method using the D&C as an embedding method for coupling an atomic cluster to its extended environment. The convergence properties as implemented within the self-consistent partial wave linear variational method (SCPW) are illustrated through various applications. In particular, results from a study of the adsorption of La atoms at the prism plane of -Si3N4 demonstrate the practicality of the SCPW using D&C as an embedding technique. PACS numbers: 71.15.Mb, 31.15.Ew, 31.50.Bc

Lattice strain effects in graphane and partially-hydrogenated graphene sheets

This paper presents a brief review of recent developments in the studies of fully hydrogenated graphene sheets, also known as graphane, and related initial results on partially hydrogenated structures. For the fully hydrogenated case, some important discrepancies, specifically whether or not the graphene sheet expands or contracts upon hydrogenation, exist between published first-principles calculations, and between calculations and experiment. The lattice change has important effects on partially hydrogenated structures. In addition, calculations of the interfacial energy must carefully account for the strain energy in neighboring regions: For sufficiently large regions between interfaces, defects at the interface which relieve the strain may be energetically preferable. Our preliminary first-principles calculations of ribbon structures, with interfaces between graphane and graphene regions, indicate that the interfaces do indeed have substantial misfit strains. Similarly, our tight-binding simulations show that at ambient temperatures, segments of graphene sheets may spontaneously combine with atomic hydrogen to form regions of graphane. Here, small amounts of chemisorbed hydrogen distort the graphene layer, due to the lattice misfit, and may induce the adsorption of more hydrogen atoms.