Theoretical calculations shed light on the adsorption of some of the most common interstellar complex organic molecules on a crystalline water ice surface, underlining the contribution of dispersive forces in accurately describing the interactions in the adsorbate/ice systems.

The interstellar medium (ISM) is extremely heterogeneous in terms of physical environments and chemical composition. Spectroscopic observations in the recent decades have revealed the presence of gaseous material and dust grains covered in ices predominantly of water in interstellar clouds, the interplay of which may elucidate the existence of more than 250 molecular species. Of these species of varied complexity, several terrestrial carbon-containing compounds have been discovered, known as interstellar complex organic molecules (iCOMs) in the astrochemical argot. In order to investigate the formation of iCOMs, it is crucial to explore gas-grain chemistry and in this regard, one of the fundamental parameters is the binding energy (BE), which is an essential input in astrochemical models. In this work, the BEs of 13 complex organic molecules on a crystalline H2O-ice surface have been computed by means of quantum chemical periodic calculations. The hybrid B3LYP-D3 DFT method was used for the geometry optimizations of the adsorbate/ice systems and for computing the BEs. Furthermore, to refine the BE values, the ONIOM2 approximation has been employed to obtain them at CCSD(T), which correlate well with those obtained at B3LYP-D3. Additionally, aiming to lower the computational cost, structural optimizations were carried out using the HF-3c level of theory, followed by single point energy calculations at B3LYP-D3 in order to obtain BE values comparable to the full DFT treatment.

This work has been published as a Book Chapter in: Kakkar, H., Martínez-Bachs, B., Rimola, A. (2022). An Ab Initio Computational Study of Binding Energies of Interstellar Complex Organic Molecules on Crystalline Water Ice Surface Models. In: Gervasi, O., Murgante, B., Misra, S., Rocha, A.M.A.C., Garau, C. (eds) Computational Science and Its Applications – ICCSA 2022 Workshops. ICCSA 2022. Lecture Notes in Computer Science, vol 13378. Springer, Cham.

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