The electronic properties of two-dimensional honeycomb structures of molybdenum disulfide (MoS 2 ) subjected to biaxial strain have been investigated using first-principles calculations based on density functional theory. On applying compressive or tensile bi-axial strain on bi-layer and mono-layer MoS 2 , the electronic properties are predicted to change from semiconducting to metallic. These changes present very interesting possibilities for engineering the electronic properties of two-dimensional structures of MoS 2 .

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Using ab initio calculations we demonstrate that extra electrons in pure amorphous SiO2 can be trapped in deep band gap states. Classical potentials were used to generate amorphous silica models and density functional theory to characterize the geometrical and electronic structures of trapped electrons. Extra electrons can trap spontaneously on pre-existing structural precursors in amorphous SiO2 and produce ≈ 3.2 eV deep states in the band gap. These precursors comprise wide (≥132 • ) O-Si-O angles and elongated Si-O bonds at the tails of corresponding distributions. The electron trapping in amorphous silica structure results in an opening of the O-Si-O angle (up to almost 180 • ). We estimate the concentration of these electron trapping sites to be ≈ 4 × 10 19 cm −3 . The structure of these centers is similar to that of Ge and Li electron centers in α-quartz.

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