Herein, we systematically studied the electronic, optical, and mechanical properties of a hydrogenated (6,0) single-walled carbon nanotube [(6,0) h-SWCNT] under applied uniaxial stress from first-principles density functional theory (DFT) and molecular dynamics (MD) simulation. We have applied the uniaxial stress range from −18 to 22 GPa on the (6,0) h-SWCNT (− sign indicates compressive and + indicates tensile stress) along the tube axes. Our system was found to be an indirect semiconductor (Γ−Δ), with a band gap value of ∼0.77 eV within the linear combination of atomic orbitals (LCAO) method using a GGA-1/2 exchangecorrelation approximation. The band gap for (6,0) h-SWCNT significantly varies with the application of stress. The indirect to direct band gap transition was observed under compressive stress (−14 GPa). The strained (6,0) h-SWCNT showed a strong optical absorption in the infrared region. Application of external stress enhanced the optically active region from infrared to Vis with maximum intensity within the Vis-IR region, making it a promising candidate for optoelectronic devices. Ab initio molecular dynamics (AIMD) simulation has been used to study the elastic properties of the (6,0) h-SWCNT which has a strong influence under applied stress.

We report the hydrogen storage properties of the bilayer h-BN/Gr heterostructure using the density functional theory calculations incorporating DFT-D2 and D3 dispersion corrections. The hydrogen molecules are adsorbed in between the two monolayers and on top of the graphene layer with a maximum gravimetric density of 5.83 wt %. The average adsorption energy per hydrogen molecules (−0.23 eV/H2) is in line with the USDOE benchmark. DFT-D3 shows an enhancement in the adsorption energy by 0.01–0.02 eV. The potentiality of the h-BN/Gr heterostructure for hydrogen storage material can be ascertained from the fact that the material can adsorb hydrogen molecules at all available sites within the binding energy limit (−0.15 to −0.60 eV/H2) without external factors such as metal decorations, electric field, or strain. The hydrogen adsorption on h-BN/Gr is highly modulated by weak van der Waals and electrostatic interactions.

In this paper, we have tried to elucidate the variation of structural, electronic, and thermodynamic properties of glasslike Na 2 GeO 3 under compressive isotropic pressure within a framework of density functional theory (DFT). The result shows stable structural (orthorhombic → tetragonal) and electronic (indirect → direct) phase transitions at P ∼ 20 GPa. The electronic band gap transition plays a key role in the enhancement of optical properties. The results of the thermodynamic properties have shown that Na 2 GeO 3 follows Debye's lowtemperature specific heat law and the classical thermodynamic of the Dulong−Petit law at high temperature. The pressure sensitivity of the electronic properties led us to compute the piezoelectric tensor (both in relaxed and clamped ions). We have observed significant electric responses in the form of a piezoelectric coefficient under applied pressure. This property suggested that Na 2 GeO 3 could be a potential material for energy harvest in future energy-efficient devices. As expected, Na 2 GeO 3 becomes harder and harder under compressive pressure up to the phase transition pressure (∼20 GPa) which can be read from Pugh's ratio (k H ) > 1.75, however, at pressures above 20 GPa k H < 1.75, which may be due to the formation of fractures at high pressure.