The ARMAGNHAC Database: A Ratio-based Molecular Analyzer and Generator of Numerous Hydrogenated Amorphous Carbons

Hydrogenated amorphous carbons (HACs) are complex, disordered forms of carbon that are of interest in various scientific fields, such as the study of air pollution from soot particles and astrochemistry. A new stochastic, structurally guided algorithm is presented for the large-scale generation of atomistic models of HACs. It consists of a two-step procedure: (i) the randomized generation of 2D structures using the SMILES (simplified molecular input line entry system) description, respecting user-predefined chemical constraints; (ii) the subsequent generation of 3D structures, making use of a stochastic sampling algorithm combined with local optimizations at the DFTB (density functional-based tight binding) level. The method was used to generate the ARMAGNHAC database (web site: https://armagnhac.laas.fr/) which provides structural (Cartesian coordinates, functional group ratios, Hill-Wheeler parameters, and aromaticity descriptors), energetic (HOMO-LUMO gap, ionization energy, and electronic affinity), and spectroscopic properties of 4366 HACs. Correlation plots between these descriptors can be generated on the web site, as well as IR spectra, possibly including their evolution as a function of a given property. Several illustrations are given, such as the dependence of the ionization potentials and electronic affinities on the size of the largest aromatic island of the HACs. The database (structures and properties) can be downloaded by users. This work paves the way for future studies aiming to derive relationships between structure, energetic, and spectral properties of HACs, as required to interpret spectral observations and experimental measurements.