Encapsulation effect of π-conjugated quaterthiophene on the radial breathing and tangential modes of semiconducting and metallic single-walled carbon nanotubes.

We developed a hybrid approach, combining the density functional theory, molecular mechanics, bond polarizability model and the spectral moment's method to compute the nonresonant Raman spectra of a single quaterthiophene (4T) molecule encapsulated into a single-walled carbon nanotube (metallic or semiconducting). We reported the optimal tube diameter allowing the 4T encapsulation. The influence of the encapsulation on the Raman modes of the 4T molecule and those of the nanotube (radial breathing modes and tangential modes) are analyzed. An eventual charge transfer between the 4T oligomer and the nanotube is discussed.

(Cu)tet(Cr2-xSnx)octS4-ySey Spinels: Crystal Structure, Density Functional Theory Calculations, and Magnetic Behavior.

A new series of (Cu)tet[Cr2-xSnx]octS4-ySey compounds was prepared by solid-state reaction at high temperature. Determination of the crystal structures by single-crystal X-ray diffraction revealed that CuCr1.0Sn1.0S2.1Se1.9, CuCr1.2Sn0.8S2.1Se1.9, CuCr1.3Sn0.7S2.2Se1.8, and CuCr1.5Sn0.5S2.2Se1.8 crystallize in a normal spinel-type structure (cubic Fd3m space group). The powder X-ray diffraction patterns and Rietveld refinements of nominal CuCr2-xSnxS2Se2 (x = 0.2, 0.4, 0.6, 0.8, and 1.0) were consistent with single-crystal X-ray diffraction data. Raman scattering analysis revealed that the A1g, Eg, and three F2g vibrational modes were observed in the spectra. The signal at ∼382 cm-1, corresponding to the A1g mode, is attributed to symmetrical stretching of the chalcogen bond with respect to the tetrahedral metal. The samples with x = 0.2 and 0.4 exhibited ferromagnetic behavior, characterized by large positive θ values of +261 and +189 K, respectively. In contrast, antiferromagnetic (AF) behavior was observed for CuCrSnS2Se2 with a Néel temperature (TN) of 18.8 K and a θ value of -36.0 K. Density functional theory (DFT) and effective magnetic moments (µeff/µtheo) experimentally measured showed that the Sn ion is in oxidation state of 4+, i.e., diamagnetic behavior. DFT calculations revealed that the most stable magnetic state of CuCr1.0Sn1.0S2Se2 was AF with exchange constants for first- and second-neighbor interactions of J1 = 56.22 cm-1 and J2 = -33.88 cm-1. Thus, the AF interactions between ferromagnetic chains in CuCr1.0Sn1.0S2Se2 originate from the presence of diamagnetic Sn cations.

Novel photobioreactor design for the culture of Dunaliella tertiolecta - Impact of color in the growth of microalgae.

Microalgae are affected by the amount of light received. This parameter can be controlled by changing the light source and altering the reactor used for their growth. In this study, the effect of different colors of light was analyzed in the growth of Dunaliella tertiolecta, observing that blue lighting systems reached a biomass 10 times superior to the one generated by orange lightning systems. This growth effect was seen in a novel tubular internally illuminated photobioreactor. In this photobioreactor, the blue reactor produced 1.7 times the biomass of the red reactor, with the particularity that the latter showed an oscillating behavior in its growth. From irradiance models, the light dispersion coefficient is higher than the absorption coefficient when using red light. In contrast, with blue light, the value of the scattering coefficient is almost null.

Sequential oxygen chemisorption on Fe13 clusters: from first-principles to practical insights.

With the advent of more precise technologies allowing manipulation of matter at nanoscopic scales and novel characterization techniques, a growing field of research is focused on magnetic materials of technical interest-such as Fe clusters-and their related physical-chemical processes. In this study, we present the results of the sequential oxidation process of the Fe13 cluster by considering the physical-chemistry properties of the ground state configurations of Fe13O n ([Formula: see text]) clusters. We develop an exhaustive ab initio study into the GGA approach and explore the effect of the chemisorption of oxygen on the structural properties, the chemical stability, the magnetization and the magnetic anisotropy energy (MAE) of the systems. Our results clearly indicate that: (i) one of the studied clusters, Fe13O17, presents the biggest electrophilicity index and the lowest chemical hardness, being the most reactive among the systems studied; (ii) the Fe13O10 exhibits a much more enhanced magnetization than other related clusters intended for health and technology applications (Sun et al 2007 J. Phys. Chem. C 111 4159-63), so that it might be a better candidate for those purposes; and (iii) the MAE presents a complex and intriguing landscape that encourages thinking about the plausible control of magnetic states focused on technical applications.

Uniaxial magnetic anisotropy energy of Fe wires embedded in carbon nanotubes.

In this work, we analyze the magnetic anisotropy energy (MAE) of Fe cylinders embedded within zigzag carbon nanotubes, by means of ab initio calculations. To see the influence of the confinement, we fix the Fe cylinder diameter and we follow the changes of the MAE as a function of the diameter of the nanotube, which contains the Fe cylinder. We find that the easy axis changes from parallel to perpendicular, with respect to the cylinder axis. The orientation change depends quite strongly on the confinement, which indicates a nontrivial dependence of the magnetization direction as function of the nanotube diameter. We also find that the MAE is affected by where the Fe cylinder sits with respect to the carbon nanotube, and the coupling between these two structures could also dominate the magnetic response. We analyze the thermal stability of the magnetization orientation of the Fe cylinder close to room temperature.

Physical and chemical characterization of Pt(12-n)Cu(n) clusters via ab initio calculations.

The physical, structural, and chemical properties of bimetallic Pt(12-n)Cu(n) clusters, where n goes from 0 to 12, have been investigated within density functional theory. We find that the electronic and magnetic properties depend a lot on the atomic fraction of Cu atoms, mainly as the number of Cu atoms changes from even to odd. The chemical potential increases monotonically as a function of the Cu concentration, whereas other chemical properties such as electrophilicity depend on local changes and decreases monotonically, as well as the ionization potential. The hardness has an oscillatory behavior, which depends on the total number of electrons. The reactivity has been spatially analyzed by studying the highest occupied molecular orbital and lowest unoccupied molecular orbital. Charge delocalization is largely increased by the number of copper atoms, whereas for largely Pt concentrations, the charge is more atomiclike. That charge dependence gives another cluster outside view, which shows a rich spatial reactivity. The magnetic dependence of the cluster on the Cu atom concentration opens the door to potential chemistry applications on bimetallic magnetic nanostructures in the field of spintronics.