Molecular‐Level Insights Into Corrosion Inhibition Efficiency of Semicarbazone Derivatives on Carbon Steel: a Synergistic DFT and DFTB Investigation

ABSTRACT This computational investigation systematically examines the corrosion inhibition effectiveness of 2‐furaldehyde semicarbazone (FSC) derivatives for carbon steel in a strongly acidic environment using an integrated density functional theory (DFT) and density functional tight binding (DFTB) approach. Initially inspired by the experimentally confirmed high inhibition performance of 5‐nitro‐2‐furaldehyde semicarbazone (FSC‐N; 88.7% inhibition efficiency at 303 K and 92.1% at 333 K), this study explores how systematic modifications of the nitro substituent (–NO 2 ) with different functional groups, hydrogen (FSC), methyl (FSC‐M), amino (FSC‐A), dimethylamino (FSC‐D), and cyano (FSC‐C), affect their electronic, structural, and adsorption properties. DFT calculations provided detailed insights into electronic structures, frontier molecular orbitals (HOMO, LUMO), energy gaps (Δ E ), and global reactivity parameters, while DFTB simulations precisely characterized optimized adsorption geometries and interaction energies on the Fe(110) surface. Among neutral species, FSC‐N exhibited the strongest adsorption (−3.257 eV), while under acidic conditions favoring protonation, FSC‐D showed the strongest adsorption (−3.268 eV) due to enhanced electrophilicity and multi‐site Fe–C coordination. Thus, FSC‐N is identified as optimal when neutral species dominate, whereas FSC‐D is most effective under strongly acidic conditions.