A. Bautista Hernández

Detection of paracetamol by armchair BN nanotubes: a molecular study

We have investigated structural and electronic properties of single wall (5,5) boron nitride nanotubes functionalized on the surface and at the ends with paracetamol (C8H9NO2). Studies have been done within the density functional theory as implemented in DMol3 quantum chemistry code. The exchange and correlation energies have been treated according to the generalized gradient approximation with the Perdew–Burke–Ernzerhof parameterization and a basis function with double polarization. The geometry optimization of the (5,5) BNNT-Paracetamol system has been done using the criterion of minimum energy considering eight possible atomic interacting configurations. Simulation results show that the preferential interaction (physisorption) site of the paracetamol is on the nanotube surface in a parallel configuration and making an angle of 45° in the perpendicular direction to the nanotube. The BNNT-Paracetamol system experiences an increase in the polarity which favors the possible dispersion and solubility. As a result of the interaction, the functionalized nanotube chemical reactivity is increased. Provided the work function of the nondoped BNNT-Paracetamol structure decreases as compared with the pristine BNNT, the functionalized nanotubes yielded conditions to improve field emission properties consequently, they may be used as biosensors of paracetamol. Finally, the nanotube doped with carbon atoms induces chemisorption and an increase in the polarity, reactivity, and reduction in the work function. Taking into account, these results it may be suggested the use of the system in sensor devices and optoelectronic systems.

Long range corrected-wPBE based analysis of the H2O adsorption on magnetic BC3 nanosheets

Density functional theory based methods were used for the analysis of the interaction between BC3 (a graphene nanosheet doped with boron), pristine and with point defects (vacancies of carbon – VC and boron – VB), and the H2O molecule. The Perdew–Burke–Ernzerhof (LC-wPBE) functional, which includes long range corrections, combined with the 6-31G(d) basis sets developed by Pople et al. was used. The results from the structural and electronic relaxation indicate that the BC3 nanosheets, pristine and with VC and VB defects, present magnetic properties. For the neutral case, they have magnetic moments of 2, 4, and 3 bohr magnetons (μB). Roughly, BC3 and BC3/VB present metallic character but BC3/VC exhibits semiconductor behavior. Adsorption of the H2O molecule on the pristine BC3 and BC3/VC nanolayers is mainly governed by van der Waals forces, yielding adsorption energies of −0.45 and −0.21 eV, respectively. In the BC3–H2O and BC3/VB–H2O systems, the water molecule is oriented in a parallel manner to the BC3 mesh, presenting equilibrium distances of 1.79 and 2.45 A, respectively. This type of functionalization may produce changes in the hybridization of such bi-dimensional structures. Remarkably, in the BC3/VC–H2O system, the water molecule is dissociated into hydroxyl and hydrogen moieties. Structural stability is achieved in the three systems (as was confirmed by vibrational analysis) and the magnetic properties are also preserved, or even enhanced. On BC3–H2O (pristine, and with VC and VB vacancies), the following was found: an increase in the polarity, low chemical reactivity and low values for the work function. Thus, BC3–H2O, BC3/VC–H2O and BC3/VB–H2O may be used for the transportation of pharmaceuticals, in optoelectronics and in the design of magnetic devices.

Ideal strength on clusters from first principles: the Ti13 case

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.

Theoretical study on small clusters of BaTiO3 using DFT calculations

Using density functional theory with the generalised gradient approximation, the structural and electronic properties of small (BaTiO3)n (n = 1–4) clusters have been studied. All the analysed growth modes were observed to consist of the same unit block, which in turn is similar to the well-known (TiO2)2 cluster. The BaTiO3 and (BaTiO3)2 systems were observed to adopt analogous geometries to the ground state of (TiO2)n clusters with Cs and D2h symmetries, respectively. The calculated value of the energy gap for the studied (BaTiO3)n clusters tends to approach that observed for its tetragonal bulk BaTiO3 counterpart when n ≥ 3 is considered; the same tendency is observed for the Ba–Ba, Ba–Ti, Ti–O and Ba–Ti interatomic distances. For all the (BaTiO3)n clusters, the structural characteristics of their respective isomers were explored.