[Display omitted] • First principles computations and Monte Carlo simulation of corrosion inhibition. • Application to the case of aminobenzoic acid, its isomers and protonated forms. • Adsorption mechanism. • In-depth investigation of the isomeric effects observed experimentally. • Adsorption is dominated by weak interactions. Ortho -, meta - and para -aminobenzoic acid (ABA) in hydrochloric acid solution are used as mild steel corrosion inhibitors. Modeled as gas-solid and acidic aqueous-solid interfaces, we investigate their performance and adsorption mechanisms using first principles methodologies and Monte Carlo simulations. Computations show that both neutral and protonated ABAs exhibit spontaneous adsorption on Fe(1 1 0) surface, which is dominated by weak interactions. We observed an inhibition efficiency isomeric effect, as established experimentally. Therefore, our work should motivate the extensive use of computational modelling and chemical reactivity indices for in-depth studies of corrosion inhibition of metals by organic compounds as those employed in industries. [ABSTRACT FROM AUTHOR]