Importance of Structural Motifs in Liquid Hydrogen Fluoride

Abstract

The investigation of liquid phases by means of accurate electronic structure methods is a demanding task due to the high computational effort. We applied second-order Møller-Plesset perturbation theory and high-level quantum chemical calculations using the coupled-cluster method with single, double and perturbative triple excitations in combination with Dunnings correlation-consistent basis sets up to quintuple ζ quality. Based on these calculations, we extrapolated the correlation energy to the basis set limit in order to improve the results even further. For comparison to the correlated electronic structure methods, density functional calculations employing different functionals are presented as well. The investigated species are a cyclic pentamer as well as a set of branched structures. The quantum cluster equilibrium method is employed for the investigation of the liquid-phase structure of hydrogen fluoride. The pentamer is found to be present to a high extent and in the case of the MP2/QZVP data, its presence improves the results significantly. Accounting for branched structures slightly improves results, so that they are found to be present but not to dominate in liquid hydrogen fluoride. Concerning both the interaction energy and the result of the quantum cluster equilibrium calculation the basis set has a major influence, whereas the difference between Møller-Plesset perturbation theory and coupled-cluster calculations is less pronounced.

Quantum cluster equilibrium model of N-methylformamide–water binary mixtures

“…They can be used to weigh single-cluster properties (e.g., number of hydrogen bonds or quadrupole coupling constants) 38,66 and measure the importance of structural motifs contained in the cluster. 65,66,84,85,89,90 Instead of particle numbers, the percentage of the total number of monomers…”

“…56,65,66,84,85,89,90 A good cluster set comprises all the important structural motifs that characterize the investigated system. This does not mean that a cluster set needs to be large, containing every imaginable cluster, but it should include each distinct structural motif (ring, chain, etc.)…”

Hydrogen Storage for Energy Application

“…About 40 % of the energy content of hydrogen can be lost due to the storage methods. Safety is also another issue with the handling of liquid hydrogen as does the car's tank integrity, when storing, pressurizing and cooling the element to such extreme temperatures [10,[16][17][18][19]. …”

“…There is a third potential solution for hydrogen storage such as (i) metal hydrides and (ii) hydrogen adsorption in metal-organic frameworks (MOFs) and carbon based systems [10,17,18].…”

“…Latter, hydrogen can be released by dehydrogenation of metal hydrides with light elements (binary hydrides and complex hydrides) because of their large gravimetric H2 densities at high temperature [10,17]. Regarding vehicle applications, metal hydrides (MHs) can be distinguished into high or low temperature materials [26].…”