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Computations based on density functional theory (DFT) were performed to get insights into the structural stability, electronic, and magnetic properties of fullerene-like boron nitride cages (f-like BNCs) for different BxNy chemical stoichiometry (x + y = 28). The results reveal at least metastable nanostructures for anionic charge (Q = -1) and doublet state (M = 2); furthermore, a magnetic moment of 1.0 bohr magneton is associated with them. These systems, in general, have high chemical stability due to their large values of cohesion energy, and the structural stability was corroborated by means of vibrational calculations. According to quantum descriptors, they exhibit high polarity (except to B27N and B28 systems), low average chemical reactivity and average work function, and electronic behavior like semiconductors. Therefore, the properties of these systems are improved compared to the B28 system, and thus the nonstoichiometry fullerenes can be used for more applications than the pristine one.
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DFT calculations were carried out in order to determine the electronic and structural properties of pentagonal Al n (I h and D 5d symmetries), Al n -CO, and Al n -NO clusters, where n = 7, 13, 19, 43, or 55 atoms. As n was increased, the bare clusters were found to exhibit a transition in electronic behavior (from semiconductor to conductor) at n = 43 atoms. Clusters with a bound CO or NO molecule also showed this behavior, although their HOMO-LUMO energy gaps were smaller than those for the corresponding bare clusters. As the size of the Al n -CO or Al n -NO cluster increased, the presence of extra p electrons improved the capacity of the cluster to adsorb a CO or NO molecule and resulted in an increase in the electronic charge directed from the aluminum atom at the adsorption site to the adsorbed species (CO or NO), thus strengthening the Al-CO or Al-NO bond. Furthermore, the Al n CO and Al n NO clusters with n = 43 and 55 exhibited chemisorption, as did the Al13-NO cluster; the other clusters presented physisorption, based on their adsorption energies. The tendency to adsorb either CO or NO increased with the size of the aluminum cluster. Graphical Abstract Adsorption of CO and NO molecules onto pentagonal clusters of aluminum: a DFT study.
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Using first principles calculations, we investigate the electronic properties of a new boron nitride based system, the graphene-like boron nitride oxide. We use the Density Functional Theory as implemented in the DMOL3 code, employing the LDA (PWC) and GGA (PBE) for the exchange-correlation term. The atomic sheets are modeled through the (N27B27H17 + (OH)3 + COOH + O) cluster, considering two cases, the OH and carboxylic groups bonded to the nitrogen atom and then bounded to boron atom. Both systems are structurally stable and the gap between the HOMO and LUMO are 1.24 y 2.36 eV, respectively, smaller than the boron nitride sheet (4.84 eV). Moreover, when the carboxylic group is bonded to the nitrogen atom, the system presents high polarity, compared with graphene oxide and with the another configuration.
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The mechanical behavior of a Ti(13) cluster, based on total energy mechanical quantum calculations is studied. The cluster geometry has been optimized and good agreement with previous reports has been found. Axial strain is applied along one of the principal axes and the changes on the energetic and vibrational properties of the system are followed. To characterize the cluster stability as a function of strain, vibrational frequencies and total energy have been calculated, to obtain the cluster maximum load tolerance for compression (C) and tensile (T). If the maximum load is defined through a vibrational instability, it happens to be two and half, and three times larger than when the maximum total energy is considered (C and T respectively). As a result of the induced strain along of the C(5) symmetry element, the cluster changes its point group symmetry from I(h) to D(5d), with an energy difference of 1.17 eV (for compression) and 0.33 eV (for tension) with respect to the ground state geometry. The electronic changes are also characterized, as function of the strain, by following the modifications of the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and changes on the total atomic population.
RESUMO
Results about stability, electronic structure and characteristic electronic properties are reported for cluster structures based on icosahedra structure with a composition of Ti12X (X = Li to Xe) within the generalized gradient approximation of the density functional theory. It is demonstrated that several elements allow an improvement on the stability of Ti13 by a doping process where the central atoms is substituted. C, Si, P, Co, Ge, Ru and Te lead to the largest gain in energy, while the HOMO-LUMO maximum gap distinguishes to just C, Si, P and Te as the most probable to be found in experimental samples. The analysis included physicochemical study of the most stable clusters to predict chemical affinity and new properties. Results reported here are in agreement with partial studies of Ti12X but because of the considered elements, a new scope is open of possible application mainly in the fields as sensors, catalysis and medicine, where the chemical selectivity is an important parameter.