Using full-potential density functional calculations within local density approximation (LDA), we predict that mechanically tunable band-gap and quasi-particle-effective-mass are realizable in graphene/hexagonal-BN hetero-bilayer (C/h-BN HBL) by application of in-plane homogeneous biaxial strain. While providing one of the possible reasons for the experimentally observed gap-less pristine-graphene-like electronic properties of C/h-BN HBL, which theoretically has a narrow band-gap, we suggest a schematic experiment for verification of our results which may find applications in nano-electromechanical systems (NEMS), nano opto-mechanical systems (NOMS) and other nano-devices based on C/h-BN HBL.

The gravitational effects in the relativistic quantum mechanics are investigated in a relativistically derived version of Heaviside's speculative gravity ( in flat space-time) named here as "Maxwellian Gravity". The standard Dirac's approach to the intrinsic spin in the fields of Maxwellian Gravity yields the gravitomagnetic moment of a Dirac (spin 1 / 2 ) particle exactly equal to its intrinsic spin. Violation of The Equivalence Principle ( both at classical and Quantum-mechanical level ) in the relativistic domain has also been reported in this work.

The ground state structural and electronic properties of germanene (the germanium analogue of graphene) are investigated using first-principles calculations. On structure optimization, the graphene-like honeycomb structure of germanene turns out as buckled (buckling parameter    Å) in contrast with graphene's planar structure (buckling parameter    Å). In spite of this, germanene has similar electronic structure as that of graphene. While corroborating the reported results, we newly predict the in-plane contraction of hexagonal Ge with (thermal) stretching along the "c" axis, akin to a phenomenon observed in graphite.

Our First-principles Full-Potential Density Functional Theory (DFT) calculations show that a monolayer of ZnS (ML-ZnS), which is predicted to adopt a graphene-like planar honeycomb structure with a direct band gap, undergoes strain-induced modifications in its structure and band gap when subjected to in-plane homogeneous biaxial strain (δ). ML-ZnS gets buckled for compressive strain greater than 0.92%; the buckling parameter ∆ (= 0.00Å for planar ML-ZnS) linearly increases with increasing compressive strain (∆ = 0.435Å at δ = −5.25%). A tensile strain of 2.91% turns the direct band gap of ML-ZnS into indirect. Within our considered strain values of |δ| < 6%, the band gap shows linearly decreasing (non-linearly increasing as well as decreasing) variation with tensile (compressive) strain. These predictions may be exploited in future for potential applications in strain sensors and other nano-devices such as the nano-electromechanical systems (NEMS).

We present ab initio calculations which show that the direct-band-gap, effective masses and Fermi velocities of charge carriers in ZnO monolayer (ML-ZnO) in graphene-like honeycomb structure are all tunable by application of in-plane homogeneous biaxial strain. Within our simulated strain limit of ±10%, the band gap remains direct and shows a strong non-linear variation with strain. Moreover, the average Fermi velocity of electrons in unstrained ML-ZnO is of the same order of magnitude as that in graphene. The results promise potential applications of ML-ZnO in mechatronics/straintronics and other nano-devices such as the nano-electromechanical systems (NEMS) and nano-optomechanical systems (NOMS).