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From: Machine learning-assisted design of carbon nanotube-based single-atom catalysts for hydrogen evolution reaction

Figure 1. Flowchart of machine learning framework for HER studies on M-N₄-CNT(n, n) catalysts. Here, Num, M, θ_d, PE, IE, EA, RM, L, and B denote the atomic number, atomic mass, d-electron count, Pauling electronegativity, first ionization energy, electron affinity, covalent radius, period, and group number of the transition metal, respectively, while n represents the carbon nanotube chirality index. DFT: Density functional theory; Num: atomic number; M: atomic mass; θ_d: d-electron count; PE: Pauling electronegativity; IE: first ionization energy; EA: electron affinity; RM: covalent radius; L: period; B: group number; SISSO: Sure Independence Screening and Sparsifying Operator; HER: hydrogen evolution reaction; CNT: carbon nanotube.