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.

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.

Under the effect of uniaxial compressive strain along [001]-direction, the electronic, magneto-optical, and electronic transport properties of double perovskite oxide were realized by substituting the Ti atom by Cr atom in Ca2TiMnO6 (CTMO). A first-principles method within the various approximations (PBEsol-GGA, GGA+U, YS-PBE0 and TB-mBJ) has been employed. The analysis of the electronic structure reveals that the compound Ca2CrMnO6 (CCMO) has a half-metallic (HM) ferromagnet (FM) nature which attributes to hybridization between Cr-3[Formula: see text], Mn-3[Formula: see text] and O-2[Formula: see text] states. CTMO exhibits an integer value of magnetic moment 3 [Formula: see text]. However, CCMO exhibits the half-metallicity (HM) under compressive strain from −2% to −5% with the total magnetic moment, a value of 5 [Formula: see text]. CCMO possesses a mediocre spin-down bandgap ([Formula: see text]2 eV) optimum for thermoelectricity and optoelectronics. The optical properties within GGA+U reveal that the CCMO can absorb light under all frequencies. We have calculated the Seebeck coefficient, and electrical and electronic thermal conductivities to determine the thermoelectric (TE) figure of merit (ZT), which is found to be approaching 1 at room temperature considering the spin-down electrons. This compound CCMO may be used for optoelectronic, solar cell, and TE applications due to its amazing properties.

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