The effect of strain on the Landau levels (LLs) spectra in graphene is studied, using an effective Dirac-like Hamiltonian which includes the distortion in the Dirac cones, anisotropy and spatial-dependence of the Fermi velocity induced by the lattice change through a renormalized linear momentum. We propose a geometrical approach to obtain the electron's wave-function and the LLs in graphene from the Sturm-Liouville theory, using the minimal substitution method. The coefficients of the renormalized linear momentum are fitted to the energy bands, which are obtained from a Density Functional Theory (DFT) calculation. In particular, we evaluate the case of Dirac cones with an ellipsoidal transversal section resulting from uniaxially strained graphene along the armchair (AC) and zig-zag (ZZ) directions. We found that uniaxial strain in graphene induces a contraction of the LLs spectra for both strain directions. Also, is evaluated the contribution of the tilting of Dirac cone axis resulting from the uniaxial deformations to the contraction of the LLs spectra.

We report a detailed theoretical investigation of the structural and electronic properties of titanium-and nickel-doped defective graphene nanoplatelets, which are shown to be efficient materials for hydrogen storage. We found that H 2 bond cleavage is favored by Ti 4 -doped defective graphene nanoplatelets because of the strong interaction between the hydrogen 1s and titanium 3d levels that leads to the formation of metal hydrides, while H 2 adsorption on Ni 4 -doped defective graphene favors the formation of Kubas complexes as hydrogen 1s levels only interact with the nickel 4s levels. A comparison between adsorption energies, number of H 2 adsorbed molecules, and hydrogen gravimetric content shows that Ti 4 -doped graphene has a better performance for hydrogen storage with a notably high hydrogen gravimetric content of 3.4 wt %; than Ni 4 -doped graphene with a 10-fold lower gravimetric content of only 0.30 wt %. This observation can be explained by three factors: Ti is a lighter transition metal, it absorbs a larger amount H 2 per metallic atom, and it presents a planar geometry that increases the coverage of the graphene layer and makes possible that all atoms in the cluster participate in the H 2 adsorption. Our results support the hypothesis that a controlled introduction of defects in graphene followed by the anchoring of small metallic clusters is a feasible way to enhance the hydrogen gravimetric content of graphene nanoplatelets and to fine-tune hydrogen absorption energies to achieve a reversible operation at ambient temperature and moderates pressures, addressing one of the main challenges of a sustainable hydrogen-based economy.

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Two new crystalline rotors 1 and 2 assembled through N−H⋅⋅⋅N hydrogen bonds by using halogenated carbazole as stators and 1,4‐diaza[2.2.2]bicyclooctane (DABCO) as the rotator, are described. The dynamic characterization through 1H T1 relaxometry experiments indicate very low rotational activation barriers (Ea) of 0.67 kcal mol−1 for 1 and 0.26 kcal mol−1 for 2, indicating that DABCO can reach a THz frequency at room temperature in the latter. These Ea values are supported by solid‐state density functional theory computations. Interestingly, both supramolecular rotors show a phase transition between 298 and 250 K, revealed by differential scanning calorimetry and single‐crystal X‐ray diffraction. The subtle changes in the crystalline environment of these rotors that can alter the motion of an almost barrierless DABCO are discussed here.