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In this article, we investigate the effect of van der Waals force in zigzag carbon nanotubes (CNTs) including single‐wall CNT (SWCNT) and double‐walled CNT (DWCNT) structures with several interaction configurations. The solid‐state density functional theory is employed to calculate the geometric optimization, normal mode frequencies, and IR and Raman spectra with the periodic boundary condition. For SWCNTs, we find that the Raman intensity is not affected by the tube diameter or the electronic structure. The IR absorption, however, increases with the tube diameter. We find that the close metallicity of the electronic structure has a significant impact on the IR simulations. When the van der Waals force is applied outside the CNTs at a distance longer than 3.0, the effect on Raman spectra is minimal but some effects can still be confirmed by IR absorption. When the van der Waals force acts inside the CNTs, the effect on the spectrum can be observed, especially at a distance of 2.8 Å, both IR and Raman can be significantly enhanced in many modes. [ABSTRACT FROM AUTHOR]

Solvent-dependent magnetism in Cu-based metal–organic frameworks (MOFs) is reported. Spin-flop magnetic behaviour occurs at different dehydrated states of MOFs. The oxygens of guest and coordinated water molecules are responsible as water removal tunes the coordination geometry around the Cu centre and the electronic structure of the framework. [ABSTRACT FROM AUTHOR]

• DFT calculations with HSE hybrid functionalreveal that SnS 2 monolayer with one or two nickel dopants can be stable with low formation energy. • The Ni doping strongly alters the electronic structure of SnS 2 , leading to the transition from the indirect band gap of pure SnS 2 to the direct band gap with narrowed size in Ni-SnS 2. • The fundamental reason is that a Ni-dopant generates new band lines at the CBM of the electronic structure due to strong orbital hybridization with states of its nearby sulfur atoms. Direct bandgap semiconductors play a critical role in optoelectronics. In this regard, SnS 2 is a two-dimensional (2D) layered semiconductor which has ignited intensive attention due to its semiconducting nature and nontoxicity. The pristine SnS 2 , however, has an indirect bandgap. For a more widespread use, it is highly desired to translate SnS 2 into direct bandgap semiconductors by controlling external parameters. Utilizing first-principles calculation methods with HSE hybrid functional, we show the possibility of indirect to direct bandgap transition in SnS 2 single layer via nickel (Ni) doping. A substitutional Ni-dopant on the tin site of SnS 2 generates new band lines at the bottom of the conduction band due to strong orbital hybridization with states of its nearby sulfur atoms. Consequently, the direct bandgap can be achieved in SnS 2 ; moreover, the bandgap size is narrowed as the number of Ni-dopants increases. [ABSTRACT FROM AUTHOR]