Search

In the realm of solid water hydrostructures, helium atoms have a tendency to occupy the interstitial spaces formed within the crystal lattice of ice structures. The primary objective of this study is to examine the stability of various ice crystals when influenced by the presence of He atoms. Presenting a first attempt at a detailed computational description of the whole energy components (guest-water, water-water, guest-guest) in the complete crystal unit cells contributes to enhancing the knowledge available about these relatively unexplored helium-water systems, which could potentially benefit future experiments. For this purpose, two different ice structures were considered: the previously established He@ice II system, and the predicted (but currently nonexistent) He@ice XVII system. One of the main features of these He-filled structures is the stability conferred by the weak van der Waals dispersion forces that occur between the host lattice and the guest atoms, in addition to the hydrogen bonds established among the water molecules. Hence, it is crucial to accurately describe these interactions. Therefore, the first part of this research is devoted examining the performance and accuracy of various semi-local and non-local DFT/DFT-D functionals, in comparison with previous experimental and/or high-level computational data. Once the best-performing DFT functional has been identified, the stability of these empty and He-filled structures, including different number of He atoms within the lattices, is analysed in terms of their structural (lattice deformation), mechanical (pressure compression effects) and energetic properties (binding and saturation energies). In this manner, the potential formation of these structures under zero temperature and pressure conditions can be evaluated, while their maximum storage capacity is also determined. The obtained results reveal that, despite the weak underlying interactions, the He encapsulation has a rather notable effect o

Clathrate hydrates have the ability to encapsulate atoms and molecules within their cavities, and thus they could be potentially large storage capacity materials. The present work studies the multiple cage occupancy effects in the recently discovered He@sII crystal. On the basis of previous theoretical and experimental findings, the stability of He(1/1)@sII, He(1/4)@sII and He(2/4)@sII crystals was analysed in terms of structural, mechanical and energetic properties. For this purpose, first-principles DFT/DFT-D computations were performed by using both semi-local and non-local functionals, not only to elucidate which configuration is the most energetically favoured, but also to scrutinize the relevance of the long-range dispersion interactions in these kinds of compounds. We have encountered that dispersion interactions play a fundamental role in describing the underlying interactions, and different tendencies were observed depending on the choice of the functional. We found that PW86PBE-XDM shows the best performance, while the non-local functionals tested here were not able to correctly account for them. The present results reveal that the most stable configuration is the one presenting singly occupied D cages and tetrahedrally occupied H cages (He(1/4)@sII) in line with the experimental observation.

The structures and energetics of Li 2+ -doped He clusters have been determined by means of evolutionary programming optimizations and classical molecular dynamics simulations. The underlying interactions in the He N Li 2+ complexes are described by sum-of-potentials ab initio-based models. The classical picture of the He atoms surrounding the cationic dimer shows a selective growth of the clusters. By analyzing spatial distribution probabilities, and single-atom evaporative energies from molecular dynamics calculations, we found pronounced drops in the computed energy for N= 2 , 4 and 6, and smaller ones for N= 10 , 13, 15, 18, 20, 22, 24, 27 and 29. The most energetic favored structure (compared to its neighbors) is found when six He atoms are attached in the Li 2+ -cation, forming He 3 -motifs at each side and leading to the formation of the first solvation shell. In turn, as extra He atoms are added, a new shell is started to form at N= 10 , with the He 3 triangles being the building blocks in all classical solid-like structural arrangements in He N Li 2+ clusters. By combining the outcome of our work on the existence of such local solvation microstructures in Li 2+ -doped He clusters together with those from previous studies on alkali ions, we may speculate that such microsolvation effects could influence the short-time solute–solvent dynamics and thus contribute to the observed slow ions’ mobility in He droplets. Graphic Abstract: [Figure not available: see fulltext.].

The dynamics of the formation of a specific clathrate hydrate as well as its thermodynamic transitions depend on the interactions between the trapped molecules and the host water lattice. The molecular-level understanding of the different underlying processes benefits not only the description of the properties of the system, but also allows the development of multiple technological applications such as gas storage, gas separation, energy transport, etc. In this work we investigate the stability of periodic crystalline structures, such as He@sI and He@sII clathrate hydrates by first-principles computations. We consider such host water networks interacting with a guest He atom using selected density functional theory approaches, in order to explore the effects on the encapsulation of a light atom in the sI/sII crystals, by deriving all energy components (guest-water, water-water, guest-guest). Structural properties and energies were first computed by structural relaxations of the He-filled and empty sI/sII unit cells, yielding lattice and compressibility parameters comparable to experimental and theoretical values available for those hydrates. According to the results obtained, the He enclathration in the sI/sII unit cells is a stabilizing process, and both He@sI and He@sII clathrates, considering single cage occupancy, are predicted to be stable whatever the XDM or D4 dispersion correction applied. Our results further reveal that despite the weak underlying interactions the He encapsulation has a rather notable effect on both lattice parameters and energetics, with the He@sII being the most energetically favorable in accord with recent experimental observations.

We performed first-principles computations to investigate guest-host/host-host effects on the encapsulation of the CO2 molecule in sII clathrate hydrates from finite-size clusters up to periodic 3D crystal lattice systems. Structural and energetic properties were first computed for the individual and first-neighbors clathrate-like sII cages, where highly accurate ab initio quantum chemical methods are available nowadays, allowing in this way the assessment of the density functional (DFT) theoretical approaches employed. The performance of exchange-correlation functionals together with recently developed dispersion-corrected schemes was evaluated in describing interactions in both short-range and long-range regions of the potential. On this basis, structural relaxations of the CO2-filled and empty sII unit cells yield lattice and compressibility parameters comparable to experimental and previous theoretical values available for sII hydrates. According to these data, the CO2 enclathration in the sII clathrate cages is a stabilizing process, either by considering both guest-host and host-host interactions in the complete unit cell or only the guest-water energies for the individual clathrate-like sII cages. CO2@sII clathrates are predicted to be stable whatever the dispersion correction applied and in the case of single cage occupancy are found to be more stable than the CO2@sI structures. Our results reveal that DFT approaches could provide a good reasonable description of the underlying interactions, enabling the investigation of formation and transformation processes as a function of temperature and pressure.

Energetics and structural properties of selected type and size He@hydrate frameworks, e.g., from regular structured ice channels to clathrate-like cages, are presented from first-principles quantum chemistry methods. The scarcity of information on He@hydrates makes such complexes challenging targets, while their computational study entails an interesting and arduous task. Some of them have been synthesized in the laboratory, which motivates further investigations on their stability. Hence, the main focus is to examine the performance and accuracy of different wave function-based electronic structure methods, such as MP2, CCSD(T), their explicitly correlated (F12) and domain-based local pair-natural orbital (DLPNO) analogs, as well as modern and conventional density functional theory (DFT) approaches, and analytical model potentials available. Different structures are considered, starting from the "simplest system"formed by a noble gas atom (such as He) and one water molecule, followed by the study of the "fundamental units"present in all ice-like and clathrate-like frameworks (such as pentamers and hexamers) and finally the description of interactions in the "building blocks"of three-dimensional (3D) ice channels (e.g., horizontal and perpendicular ice II and Ih) and clathrate-like cages, such as the 512 present in the most common sI, sII, and sH clathrate-hydrate structures. The idea is to provide well-converged DLPNO-CCSD(T) and DFMP2/CBS reference datasets that in turn are used to validate how DFT functionals (in total, 29 approaches from generalized-gradient approximation (GGA), meta-GGA, to hybrid and range-separated functionals, including dispersion correction treatments, were checked) and analytical semiempirical/ab initio-based potentials perform compared with high-level alternatives. Within all tested approaches, those best-performing were identified and classified. Most of the DFT/DFT-D functionals, as well as available analytical pairwise model potentials

La implantación en España de la comunicación institucional y empresarial o, en términos anglosajones, las relaciones públicas ha sido muy tardía por la pervivencia de la dictadura franquista hasta hace apenas cuatro décadas, en contraposición a los Estados Unidos, país pionero en el desarrollo de las estrategias comunicativas en las organizaciones. Así, en el caso concreto de las Islas Canarias, la disciplina no empezó a dar señales de vida con unas mínimas dosis de profesionalidad en los ayuntamientos hasta bien avanzados los años noventa del pasado siglo, cuando los grupos gobernantes de los más pujantes comenzaron a desarrollar y diversificar sus áreas de comunicación para atender sus necesidades internas y las demandas de la naciente sociedad democrática. Sobre tales bases, nos hemos propuesto analizarla implantación y evolución de la actividad en el microespacio que configura la comarca tinerfeña de Abona, cuyos seis municipios, Arona, Granadilla, San Miguel, Arico, Fasnia y Vilaflor, son representativos de los desiguales grados de desarrollo socioeconómico de la realidad insular en la actualidad. Con este trabajo se pretende poner en valor el emergente campo científico de la comunicación y demostrar la relevancia de la gestión comunicativa eficiente en el ámbito específico de las corporaciones locales.

La implantación en España de la comunicación institucional y empresarial o, en términos anglosajones, las relaciones públicas ha sido muy tardía por la pervivencia de la dictadura franquista hasta hace apenas cuatro décadas, en contraposición a los Estados Unidos, país pionero en el desarrollo de las estrategias comunicativas en las organizaciones. Así, en el caso concreto de las Islas Canarias, la disciplina no empezó a dar señales de vida con unas mínimas dosis de profesionalidad en los ayuntamientos hasta bien avanzados los años noventa del pasado siglo, cuando los grupos gobernantes de los más pujantes comenzaron a desarrollar y diversificar sus áreas de comunicación para atender sus necesidades internas y las demandas de la naciente sociedad democrática. Sobre tales bases, nos hemos propuesto analizarla implantación y evolución de la actividad en el microespacio que configura la comarca tinerfeña de Abona, cuyos seis municipios, Arona, Granadilla, San Miguel, Arico, Fasnia y Vilaflor, son representativos de los desiguales grados de desarrollo socioeconómico de la realidad insular en la actualidad. Con este trabajo se pretende poner en valor el emergente campo científico de la comunicación y demostrar la relevancia de la gestión comunicativa eficiente en el ámbito específico de las corporaciones locales.

La implantación en España de la comunicación institucional y empresarial o, en términos anglosajones, las relaciones públicas ha sido muy tardía por la pervivencia de la dictadura franquista hasta hace apenas cuatro décadas, en contraposición a los Estados Unidos, país pionero en el desarrollo de las estrategias comunicativas en las organizaciones. Así, en el caso concreto de las Islas Canarias, la disciplina no empezó a dar señales de vida con unas mínimas dosis de profesionalidad en los ayuntamientos hasta bien avanzados los años noventa del pasado siglo, cuando los grupos gobernantes de los más pujantes comenzaron a desarrollar y diversificar sus áreas de comunicación para atender sus necesidades internas y las demandas de la naciente sociedad democrática. Sobre tales bases, nos hemos propuesto analizarla implantación y evolución de la actividad en el microespacio que configura la comarca tinerfeña de Abona, cuyos seis municipios, Arona, Granadilla, San Miguel, Arico, Fasnia y Vilaflor, son representativos de los desiguales grados de desarrollo socioeconómico de la realidad insular en la actualidad. Con este trabajo se pretende poner en valor el emergente campo científico de la comunicación y demostrar la relevancia de la gestión comunicativa eficiente en el ámbito específico de las corporaciones locales.

La implantación en España de la comunicación institucional y empresarial o, en términos anglosajones, las relaciones públicas ha sido muy tardía por la pervivencia de la dictadura franquista hasta hace apenas cuatro décadas, en contraposición a los Estados Unidos, país pionero en el desarrollo de las estrategias comunicativas en las organizaciones. Así, en el caso concreto de las Islas Canarias, la disciplina no empezó a dar señales de vida con unas mínimas dosis de profesionalidad en los ayuntamientos hasta bien avanzados los años noventa del pasado siglo, cuando los grupos gobernantes de los más pujantes comenzaron a desarrollar y diversificar sus áreas de comunicación para atender sus necesidades internas y las demandas de la naciente sociedad democrática. Sobre tales bases, nos hemos propuesto analizarla implantación y evolución de la actividad en el microespacio que configura la comarca tinerfeña de Abona, cuyos seis municipios, Arona, Granadilla, San Miguel, Arico, Fasnia y Vilaflor, son representativos de los desiguales grados de desarrollo socioeconómico de la realidad insular en la actualidad. Con este trabajo se pretende poner en valor el emergente campo científico de la comunicación y demostrar la relevancia de la gestión comunicativa eficiente en el ámbito específico de las corporaciones locales.