Robust Binding Energy Distribution Sampling on Amorphous Solid Water Models. Method Testing and Validation With NH3, CO and CH4

This work aims to develop a method based on a structurally reliable ice model and a statistically and physico-chemically robust approach for BE distribution inference, with the aim to be applicable to various relevant interstellar species.

A multiscale computational approach is presented, with a Molecular Dynamics (MD) Heat & Quench protocol for the amorphous water ice model, and an ONIOM(B3LYP-D3(BJ)/6-311+G**:GFN2-xtb) scheme for the BE inference, with a prime emphasis onto the BE/real system size convergence. The sampling of the binding configurations is twofold, exploring both regularly spaced binding sites, as well as various adsorbate-to-substrate orientations on each locally distinct site.

This second source of BE diversity accounts for the local roughness of the potential energy landscape of the substrate. Three different adsorbate test cases are considered, i.e. NH₃, CO and CH₄, owing to their significance in dust icy mantles, and their distinct binding behavior with water ices.

The BE distributions for NH₃, CO and CH₄ have been inferred, with converged statistics. The distribution for NH3 is better represented by a double Gaussian component profile. Three starting adsorbate orientations per site are required to reach convergence for both Gaussian components of NH₃, while 2 orientations are sufficient for CO, and one unique for CH₄ (symmetric).

Further geometrical and molecular surrounding insights have been provided. These results encompass previously reported results.

Maria Groyne, Benoît Champagne, Cedric Baijot, Michaël De Becker

Comments: Accepted for publication in A&A 22 pages, 27 Figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2504.18435 [astro-ph.IM] (or arXiv:2504.18435v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2504.18435
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Submission history
From: Maria Groyne
[v1] Fri, 25 Apr 2025 15:45:54 UTC (3,524 KB)
https://arxiv.org/abs/2504.18435
Astrobiology, Astrochemistry,