Electronic and Magnetic Properties of Zigzag Boron-Nitride Nanoribbons with Even and Odd-Line Stone-Wales (5–7 Pair) Defects

Spin-polarized first-principles calculations have been performed on zigzag boron–nitride nanoribbons (z-BNNRs) with lines of alternating fused pentagon (P) and heptagon (H) rings (pentagon–heptagon line defect) at a single edge as well as at both edges. The number of lines (<i>n</i>) of the pentagon–heptagon defect has been varied from 1 to 8 for 10-zBNNRs. Among the different spin-configurations that we have studied, we find that the spin-configuration with ferromagnetic ordering at each edge and antiferromagnetic ordering across the edges is quite interesting. For this spin-configuration, we find that, if the introduced PH line defect is odd-numbered, the systems behave as spin-polarized semiconductors, but, for even-numbered, all the systems show interesting antiferromagnetic half-metallic behavior. Robustness of these results has been cross checked by the variation of the line-defect position and also by the variation of the width [from ∼1.1 nm (6-zBNNR) to ∼3.3 nm (16-zBNNR)] of the ribbon. Density of states (DOS), projected DOS, and band-structure analysis have been accomplished to understand the reasons for these differences between even and odd line defects. The main reason for many of the observed changes was traced back to the change in edge nature of the BNNR, which indeed dictates the properties of the systems

Quasi-Diabatic Representation for Nonadiabatic Dynamics Propagation

We develop a nonadiabatic dynamics propagation scheme that allows interfacing diabatic quantum dynamics methods with commonly used adiabatic electronic structure calculations. This scheme uses adiabatic states as the quasi-diabatic (QD) states during a short-time quantum dynamics propagation. At every dynamical propagation step, these QD states are updated based on a new set of adiabatic basis. Using the partial linearized density matrix (PLDM) path-integral method as one specific example for diabatic dynamics approaches, we demonstrate the accuracy of the QD scheme with a wide range of model nonadiabatic systems as well as the on-the-fly propagations with density functional tight-binding (DFTB) calculations. This study opens the possibility to combine accurate diabatic quantum dynamics methods with adiabatic electronic structure calculations for nonadiabatic dynamics propagations

The interaction of halogen molecules with SWNTs and graphene

The interaction of halogen molecules of varying electron affinity, such as iodine monochloride (ICl), bromine (Br(2)), iodine monobromide (IBr) and iodine (I(2)) with single-walled carbon nanotubes (SWNTs) and graphene has been investigated in detail. Halogen doping of the two nanocarbons has been examined using Raman spectroscopy in conjunction with electronic absorption spectroscopy and extensive theoretical calculations. The halogen molecules, being electron withdrawing in nature, induce distinct changes in the electronic states of both the SWNTs and graphene, which manifests with a change in the spectroscopic signatures. Stiffening of the Raman G-bands of the nanocarbons upon treatment with the different halogen molecules and the emergence of new bands in the electronic absorption spectra, both point to the fact that the halogen molecules are involved in molecular charge-transfer with the nanocarbons. The experimental findings have been explained through density functional theory (DFT) calculations, which suggest that the extent of charge-transfer depends on the electron affinities of the different halogens, which determines the overall spectroscopic properties. The magnitude of the molecular charge-transfer between the halogens and the nanocarbons generally varies in the order ICl > Br(2) > IBr > I(2), which is consistent with the expected order of electron affinities

Nitrogen-Doped Graphene Quantum Dots as Possible Substrates to Stabilize Planar Conformer of Au₂₀ over Its Tetrahedral Conformer: A Systematic DFT Study

Utilizing the strengths of nitrogen-doped graphene quantum dot (N-GQD) as a substrate, herein, we have shown that one can stabilize the catalytically more active planar Au₂₀ (P-Au₂₀) compared with the thermodynamically more stable tetrahedral structure (T-Au₂₀) on an N-GQD. Clearly, this simple route avoids the usage of traditional transition-metal oxide substrates, which have been suggested and used for stabilizing the planar structure for a long time. Considering the experimental success in the synthesis of N-GQDs and in the stabilization of Au nanoparticles on N-doped graphene, we expect our proposed method to stabilize planar structure will be realized experimentally and will be useful for industrial level applications