The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Murray S Daw - One of the best experts on this subject based on the ideXlab platform.
-
topological description of the stone wales Defect Formation Energy in carbon nanotubes and graphene
Physical Review B, 2009Co-Authors: Elif Ertekin, D C Chrzan, Murray S DawAbstract:We develop a topological continuum framework to compute the Formation energies of Stone-Wales Defects in graphene and carbon nanotubes. Our approach makes no a priori assumptions about the analytical form of the dislocation strain fields while explicitly accounting for boundary conditions and Defect-Defect interactions. The continuum formalism reproduces trends observed in the atomistic simulations remarkably well and demonstrates the necessity of considering long-ranged effects to accurately describe Defect energetics in graphenebased systems.
Elif Ertekin - One of the best experts on this subject based on the ideXlab platform.
-
topological description of the stone wales Defect Formation Energy in carbon nanotubes and graphene
Physical Review B, 2009Co-Authors: Elif Ertekin, D C Chrzan, Murray S DawAbstract:We develop a topological continuum framework to compute the Formation energies of Stone-Wales Defects in graphene and carbon nanotubes. Our approach makes no a priori assumptions about the analytical form of the dislocation strain fields while explicitly accounting for boundary conditions and Defect-Defect interactions. The continuum formalism reproduces trends observed in the atomistic simulations remarkably well and demonstrates the necessity of considering long-ranged effects to accurately describe Defect energetics in graphenebased systems.
Roberto Dovesi - One of the best experts on this subject based on the ideXlab platform.
-
Comparison between cluster and supercell approaches: the case of Defects in diamond
Theoretical Chemistry Accounts, 2017Co-Authors: Simone Salustro, Roberto Orlando, Anna Maria Ferrari, Roberto DovesiAbstract:The results produced by the cluster and the supercell approaches, when applied to the study of the vacancy and $$\langle 100\rangle$$ ⟨ 100 ⟩ split self-interstitial Defects in diamond, are critically compared. The same computer code, Crystal , basis set and DFT functional (the hybrid B3LYP) are used. Clusters of increasing size (from 35 to 969 C atoms) are considered, and the results compared to those from a supercell containing $$128\pm 1$$ 128 ± 1 atoms, for which the interaction between Defects in different cells can be considered negligible. It is shown that geometry and Energy data (atomic relaxation, Defect Formation Energy, relative Energy between different spin states) show a very local nature and then converge rapidly with the cluster size. Other properties, frequently used for the characterization of the Defects using relatively small clusters (band gaps, impurity Energy levels in the gap, Raman spectra), converge slowly and, also at the limit of the very large clusters here considered, still differ from the periodic counterpart.
-
A super-cell approach for the study of localized Defects in solids: carbon substitution in bulk silicon
Journal of Physics: Condensed Matter, 1994Co-Authors: Roberto Orlando, Roberto Dovesi, P Azavant, Nicholas M. Harrison, V R SaundersAbstract:Carbon substitution in bulk silicon has been investigated using the super-cell approach, in conjunction with the periodic ab initio Hartree-Fock method. The convergence of the Defect Formation Energy and of the relaxed Defect geometry as a function of the super-cell size is discussed with reference to super-cells containing 8, 16, 32 and 64 atoms. It turns out that the convergence of the unrelaxed Defect Formation Energy is rapid, in spite of the large local charge redistribution around the Defect (the net charge on carbon is 1.2 mod e mod ); the relaxation effects are very large (about 2.0 eV) and involve mainly the first and second neighbours; however, the relaxation of the fifth neighbours of the Defect (which is possible only with the biggest super-cell considered) lowers the Energy by a further 0.06 eV. The Defect Formation Energy and the atomic displacements obtained with the 32 and 64 atoms super-cells are similar, whereas the Energy difference between the 16 and 32 atoms cells is as large as 0.4 eV.
-
Convergence properties of the supercell approach in the study of local Defects in solids
Phase Transitions, 1994Co-Authors: Roberto Dovesi, R. OrlandoAbstract:Abstract The “supercell” scheme is applied to the study of local Defects in MgO (Ca substitution, cation and anion vacancies) and bulk silicon (carbon substitution). The trend of the quantities of interest (Defect Formation Energy, geometrical relaxation, charge distribution around the Defect) as a function of the supercell size is explored; when neutral Defects are considered, supercells containing 50 to 100 atoms are large enough to allow for most of the nuclear and electronic relaxation and to produce a negligible interaction between Defects in different cells. These conclusions apply both to ionic and covalent host crystals. Present day ab initio quantum mechanical periodic computer programs can handle cells of such a size at a relatively low cost and high numerical accuracy. When charged Defects are considered (vacancies in MgO), the supercell scheme must be modified in order to avoid Coulomb divergencies, but the usually adopted correction, which consists in introducing a compensating uniform backgr...
D C Chrzan - One of the best experts on this subject based on the ideXlab platform.
-
topological description of the stone wales Defect Formation Energy in carbon nanotubes and graphene
Physical Review B, 2009Co-Authors: Elif Ertekin, D C Chrzan, Murray S DawAbstract:We develop a topological continuum framework to compute the Formation energies of Stone-Wales Defects in graphene and carbon nanotubes. Our approach makes no a priori assumptions about the analytical form of the dislocation strain fields while explicitly accounting for boundary conditions and Defect-Defect interactions. The continuum formalism reproduces trends observed in the atomistic simulations remarkably well and demonstrates the necessity of considering long-ranged effects to accurately describe Defect energetics in graphenebased systems.
Su Huai Wei - One of the best experts on this subject based on the ideXlab platform.
-
Self-regulation of charged Defect compensation and Formation Energy pinning in semiconductors.
Scientific reports, 2015Co-Authors: Ji Hui Yang, Wan-jian Yin, Ji-sang Park, Su Huai WeiAbstract:Current theoretical analyses of Defect properties without solving the detailed balance equations often estimate Fermi-level pinning position by omitting free carriers and assume Defect concentrations can be always tuned by atomic chemical potentials. This could be misleading in some circumstance. Here we clarify that: (1) Because the Fermi-level pinning is determined not only by Defect states but also by free carriers from band-edge states, band-edge states should be treated explicitly in the same footing as the Defect states in practice; (2) Defect Formation Energy, thus Defect density, could be pinned and independent on atomic chemical potentials due to the entanglement of atomic chemical potentials and Fermi Energy, in contrast to the usual expectation that Defect Formation Energy can always be tuned by varying the atomic chemical potentials; and (3) the charged Defect compensation behavior, i.e., most of donors are compensated by acceptors or vice versa, is self-regulated when Defect Formation energies are pinned. The last two phenomena are more dominant in wide-gap semiconductors or when the Defect Formation energies are small. Using NaCl and CH3NH3PbI3 as examples, we illustrate these unexpected behaviors. Our analysis thus provides new insights that enrich the understanding of the Defect physics in semiconductors and insulators.
-
chemical trends of Defect Formation in si quantum dots the case of group iii and group v dopants
Physical Review B, 2007Co-Authors: Junwei Luo, Jianbai Xia, Su Huai WeiAbstract:Using first-principles methods, we have systematically calculated the Defect Formation energies and transition Energy levels of group-III and group-V impurities doped in H passivated Si quantum dots (QDs) as functions of the QD size. The general chemical trends found in the QDs are similar to that found in bulk Si. We show that Defect Formation Energy and transition Energy level increase when the size of the QD decreases; thus, doping in small Si QDs becomes more difficult. ${\mathrm{B}}_{\mathrm{Si}}$ has the lowest acceptor transition Energy level, and it is more stable near the surface than at the center of the H passivated Si QD. On the other hand, ${\mathrm{P}}_{\mathrm{Si}}$ has the smallest donor ionization Energy, and it prefers to stay at the interior of the H passivated Si QD. We explained the general chemical trends and the dependence on the QD size in terms of the atomic chemical potentials and quantum confinement effects.
