Ab initio Calculation of Binding Energies of Interstellar Sulphur-Containing Species on Crystalline Water Ice Models

There are different environments in the interstellar medium (ISM), depending on the density, temperature and chemical composition. Among them, molecular clouds, often referred to as the cradle of stars, are paradigmatic environments relative to the chemical diversity and complexity in space. Indeed, there, radio to far-infrared observations revealed the presence of several molecules in the gas phase, while near-infrared spectroscopy detected the existence of submicron sized dust grains covered by H2O-dominated ice mantles. The interaction between gas-phase species and the surfaces of water ices is measured by the binding energy (BE), a crucial parameter in astrochemical modelling. In this work, the BEs of a set of sulphur-containing species on water ice mantles have been computed by adopting a periodic ab initio approach using a crystalline surface model. The Density Functional Theory (DFT)-based B3LYP-D3(BJ) functional was used for the prediction of the structures and energetics. DFT BEs were refined by adopting an ONIOM-like procedure to estimate them at CCSD(T) level toward complete basis set extrapolation, in which a very good correlation between values has been found. Moreover, we show that geometry optimization with the computationally cheaper HF-3c method followed by single point energy calculations at DFT to compute the BEs is a suitable cost-effective recipe to arrive at BE values of the same quality as those computed at full DFT level. Finally, computed data were compared with the available literature data

In Silico Study of Hydroxyapatite and Bioglass®: How Computational Science Sheds Light on Biomaterials

In the present Chapter it has been explained how crucial the computational techniques arewhen applied together with experimentalist measurements in the understanding ofbiological complex systems and mechanisms dealing with biomaterials for a large numberof reasons. Indeed, computational methods are extremely powerfully applied to predictstructure formation and crystal growth as well as to describe at a molecular level the realinteractions responsible of the attachment of the inorganic biomaterial to the organic tissue.In the investigation of phenomena related to a complex system such as the human body,many approximations are required, so a reductionist approach is employed also in thecomputational analysi

Water interaction with Fe2NiP Schreibersite (110) surface : a quantum mechanical atomistic perspective

Phosphorus is an element of primary importance for all living creatures, being present in many biological activities in the form of phosphate (PO43-). However, there are still open questions about the origin of this specific element and on the transformation that allowed it to be incorporated in biological systems. The most probable source of prebiotic phosphorus is the intense meteoritic bombardment during the Archean era, a few million years after the solar system formation, which brought tons of iron-phosphide materials (schreibersite) on the early Earth crust. It was recently demonstrated that by simple wetting/corrosion processes from this material, various oxygenated phosphorus compounds are produced. In the present work, the wetting process of schreibersite (Fe2NiP) was studied by computer simulations using density functional theory, with the PBE functional supplemented with dispersive interactions through a posteriori empirical correction. To start disentangling the complexity of the system, only the most stable (110) surface of Fe2NiP was used simulating different water coverages, from which structures, water binding energies, and vibrational spectra have been predicted. The computed (ana-)harmonic infrared spectra have been compared with the experimental ones, thus, confirming the validity of the adopted methodology and models

Computational Surface Modelling of Ices and Minerals of Interstellar Interest-Insights and Perspectives

The universe is molecularly rich, comprising from the simplest molecule (H2) to complex organic molecules (e.g., CH3CHO and NH2CHO), some of which of biological relevance (e.g., amino acids). This chemical richness is intimately linked to the different physical phases forming Solar-like planetary systems, in which at each phase, molecules of increasing complexity form. Interestingly, synthesis of some of these compounds only takes place in the presence of interstellar (IS) grains, i.e., solid-state sub-micron sized particles consisting of naked dust of silicates or carbonaceous materials that can be covered by water-dominated ice mantles. Surfaces of IS grains exhibit particular characteristics that allow the occurrence of pivotal chemical reactions, such as the presence of binding/catalytic sites and the capability to dissipate energy excesses through the grain phonons. The present know-how on the physicochemical features of IS grains has been obtained by the fruitful synergy of astronomical observational with astrochemical modelling and laboratory experiments. However, current limitations of these disciplines prevent us from having a full understanding of the IS grain surface chemistry as they cannot provide fundamental atomic-scale of grain surface elementary steps (i.e., adsorption, diffusion, reaction and desorption). This essential information can be obtained by means of simulations based on computational chemistry methods. One capability of these simulations deals with the construction of atom-based structural models mimicking the surfaces of IS grains, the very first step to investigate on the grain surface chemistry. This perspective aims to present the current state-of-the-art methods, techniques and strategies available in computational chemistry to model (i.e., construct and simulate) surfaces present in IS grains. Although we focus on water ice mantles and olivinic silicates as IS test case materials to exemplify the modelling procedures, a final discussion on the applicability of these approaches to simulate surfaces of other cosmic grain materials (e.g., cometary and meteoritic) is given

Ab-initio computational study on Fe2NiP schreibersite : bulk and surface characterization

Phosphorus is ubiquitous in planet Earth and plays a fundamental role in all living systems. Finding a reasonable prebiotic source of phosphorus is not trivial, as common sources where it is present nowadays are in the form of phosphate minerals, which are rather insoluble and nonreactive materials, making it unavailable for ready incorporation in living organisms. A possible source of phosphorus is from exogenous meteoritic bombardment and, in particular, iron/nickel phosphides. These materials, by simple interaction with water, produce oxygenated phosphorus compounds, which can easily react with organic molecules, thus forming C-O-P bonds. In the present work, periodic ab initio simulations at the PBE level (inclusive of dispersion interactions) have been carried out on metallic Fe2NiP schreibersite, as a relatively abundant component of metallic meteorites, in order to characterize the structural, energetic, and vibrational properties of both bulk and surfaces of this material. The aim is to study the relative stability among different surfaces and also to characterize the nanocrystal morphology of the mineral