In this report, a density functional theory (DFT) computational approach was used to investigate the structural and electronic properties of molecular hydrogens adsorbed on single-walled boron nitride nanotubes (BNNTs) with/without doped by group IV elements, such as carbon (C), silicon (Si), and germanium (Ge) atom. The twelve hydrogen molecules (H2) were added to the outer surfaces of BNNT frameworks. Geometry optimization calculations were performed to find the local energy minima of the BNNTs nanostructures with the molecular hydrogens at the DFT/B3LYP/6-31G level of theory. By employing single-point calculations at the B3LYP/6-31G* level of theory, the equilibrium geometric structures were then utilized to find the electronic structures of hydrogen molecules adsorbed on the surfaces of BNNT frameworks. The results showed that the bond lengths of B-N are in the range of1.44 Å – 1.48 Å. The optimized distances of hydrogen molecules from the surfaces of BNNTs were predicted to be 3.1 Å – 3.2 Å. Moreover, the computed HOMO-LUMO energies of molecular hydrogens adsorbed on the surface of BNNTs are about 2.2 eV – 4.3 eV. For the surface map of HOMO, the electron density distribution of hydrogen molecules adsorbed on the surface of pristine BNNT was localized in the N-tip. While in the case of doped BNNTs, the electron densities of HOMOs were focused on the group IV elements. The B-tips on the pristine and doped BNNTs possess the major contribution to the LUMO.
In this work, density functional theory (DFT) calculations were conducted to study the structural and electronic properties of pure, vacancy, and group IV [i.e. carbon (C), silicon (Si), and germanium (Ge) atoms] doped boron nitride nanotubes (BNNTs). The DFT computational results obtained agree well with the literature results. The calculated B−N bond distances obtained in this study are about 1.44 Å – 1.47 Å. Among seven BNNTs, the optimized B35GeN36H12 holds the lowest local energy minimum value in this study Moreover, the structure of B35CN36H12 possesses the smallest HOMO−LUMO energy (2.17 eV) among nine BNNT models considered. The boron (B) atoms hold the positive charges, and the negative charges fall on the nitrogen (N) atoms in this work. Similar results are reported to the molecular electrostatic potentials (MEPs) of studied BNNTs. The distributions of positive and negative electrostatic potentials fall on the regions of N− and B−tips of BNNT frameworks, respectively in this report. The DFT calculations reported that the spin densities were mainly concentrated in the regions around group IV elements, such as C, Si, and Ge atoms. Therefore, we believe that these computed results will provide useful information on the adsorption of hydrogen molecules on the BNNT frameworks in the future.
In this study, we reported the adsorption of two hydrogen (H2) molecules on six boron nitride (BN) studied models with or without adopted by one of the elements from Group IV. By employing the computational method of density functional theory (DFT), the hydrogen binding energies and electronic structures were analyzed and discussed. The computed results presented that the most favorable adsorption sites were found for the two H2 molecules in all studied systems. The computed optimal binding energies of all BN studied systems were determined to be 0.01 eV – 0.05 eV per H2 molecule, which is smaller than that of the previous literature study. Moreover, the energies of HOMO–LUMOs were predicted in the range of 1.64 eV – 6.18 eV. For the surface plots of molecular electrostatic potentials (MEPs), the H atoms at the N–edges possess the most positive electrostatic potentials, while the negative electrostatic potentials fall in the atoms of H at the B–edges. A similar trend was presented on the distribution of atomic charge. Using the scheme of Mulliken population analysis (MPA), there are two different charge values on the atom of H in this study. The H atoms at the B–edges possess the negative charges, whereas the positive charge values were found on the atoms of H at the N–edges. In addition, the findings also noted that the positive charge values were presented for all B atoms in the study. While the negative charges fall in the atoms of N.
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