Molecular Dynamics and Quantum Chemical Calculation for 3,4-Dihydropyrimidin-2(1H)-Ones As Corrosion Inhibitors of Mild Steel in 1M Hydrochloric Acid Solution

Molecular dynamics (MD) simulations and quantum chemical calculations were used to study the adsorption and the corrosion inhibition of three 3,4-dihydropyrimidin-2(1H)-ones (DHPM-1 similar to 3) on Fe(0 0 1) surface in pure water and 1 M hydrochloric acid solution. The MD simulation results indicate the three molecules are inclined to adsorbed on the Fe(0 0 1) surface, and the heterocyclic rings of the molecules are parallel to the Fe surface, while the benzene rings of three molecules point out to the aqueous side. Among the three inhibitor molecules, 5-acetyl-6-methyl-4-(3-nitro phenyl)-3,4-dihydropyrimidin- 2(1H)-one (DHPM-2) has the highest binding energy, the largest deformation energy, the largest coverage effect of single molecule, and consequentially the largest adsorption inclination on Fe(0 0 1) substrate, furthermore, the molecule has larger binding energy in 1M HC1 solution than in pure water, its combination with Fe surface is mainly the contribution from the VanderWals energy; the quantum calculations demonstrate that DHPM-2 has the lower E-LUMO, the smaller energy gap Delta E, and the largest dipole moment mu, which suggest it will interact with Fe atoms more actively. All of these imply that the better inhibition efficiency of DHPM-2 can be anticipated among these three molecules.