Starting from an anomalous monomeric system, where particles interact via a two-scale core-softened potential, we investigate how the system properties evolve inasmuch as particles are put together to form polymers whose chain size varies from 4 up to 32 monomers. We observed that the density and diffusion anomaly regions in the pressure versus temperature phase diagram of the monomeric system is smaller in the monomeric system when compared with the polymers. We also found that the polymers do not fold into themselves to form solid spheres instead they tend to maximize the chain-fluid contact. Also, Rouse and Reptation models can be employed to describe the polymers diffusive behaviour. But, in contrast to results of simulations where mere interacts via Lennard-Jones potentials, our results shown a much shorter entanglement length of at most 8 monomers.
Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectroscopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens.
The chromism observed in the MEH-PPV polymer in tetrahydrofuran (THF) solution is discussed as a function of the structural morphology of the backbone chains. To evaluate this phenomenon, we carried out simulations employing a hybrid methodology using molecular dynamics and quantum mechanical approaches. Our results support the hypothesis that the morphological order–disorder transition is related to the change from red to blue phase observed experimentally. The morphological disorder is associated with total or partial twisted arrangements in the polymer backbone, which induces an electronic conjugation length more confined to shorter segments. In addition, the main band of the MEH-PPV UV–Vis spectrum at the lower wavelength is related to the blue phase, in contrast to the red phase found for the more planar backbone chains.
We consider the transverse magnetic moment and torque observed by Li et al. (Nat. Phys. 7, 762 (2011)) in the LaAlO3/SrTiO3 interface and the theoretical model for it based on the zero helicity states. The transverse magnetic moment is explained in terms of an asymmetry between the two sides of the interface. We show here that there is an intrinsic magnetization which gives rise to a mass anisotropy in each side of the interface.
We employed PBE and BLYP semi-local functionals and the van der Waals density functional of Dion et al. (2004) (vdW-DF) to investigate structural properties of liquid acetonitrile and methanol. Among those functionals the vdW-DF is the only one that correctly predicts energy minima in inter-molecular interactions between acetonitrile molecules. We found that van der Waals interactions have a negligible effect on H-bonds in methanol chains. However, it significantly increases chain packing resulting in a more dense liquid in comparison to the other two functionals. The overall trend is that the vdW-DF tends to overestimate density and bulk modulus, meanwhile the semi-local functionals tend to underestimate density. Thus, van der Waals interactions play an important role in the properties of liquids in which much stronger dipole-dipole interactions are present.
Calcium phosphates are suggested as a CO2 adsorbent via pressure swing adsorption. Amorphous calcium phosphate (ACP) and biphasic calcium phosphate (BCP) (composed of hydroxyapatite and beta-tricalcium phosphate) were investigated for the capture/immobilization of the gas. A fluidized bed was set up to assess the levels of CO2 adsorption by ACP and BCP. A gaseous mixture was synthesized, mimicking the conditions for possible industrial use. The results show a significant reduction in CO2 concentrations. Using DFT calculations, we show that CO2 adsorption increases the stability by reducing the surface energy. The energies involved and preferential adsorption sites were also theoretically predicted.
Phenazine derivative molecules were studied using steady state and time resolved fluorescence techniques and demonstrated to lead to strong formation of aggregated species, identified as dimers by time dependent density functional theory calculations. Blended films in a matrix of Zeonex®, produced at different concentrations, showed different contributions of dimer and monomer emissions in a prompt time frame, e.g. less than 50 ns. In contrast, the phosphorescence (e.g. emission from the triplet state) shows no significant effect on dimer formation, although strong dependence of the phosphorescence intensity on concentration is observed, leading to phosphorescence being quenched at higher concentration.
A cosmological extension of the Eisenhart–Duval metric is constructed by incorporating a cosmic scale factor and the energy-momentum tensor into the scheme. The dynamics of the spacetime is governed by the Ermakov–Milne–Pinney equation. Killing isometries include spatial translations and rotations, Newton–Hooke boosts and translation in the null direction. Geodesic motion in Ermakov–Milne–Pinney cosmoi is analyzed. The derivation of the Ermakov–Lewis invariant, the Friedmann equations and the Dmitriev–Zel'dovich equations within the Eisenhart–Duval framework is presented.