## 3 Results and Discussions
### Computational Methods
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Inhibitor** & **E\({}_{\text{HOMO}}\), eV** & **E\({}_{\text{LUMO}}\), eV** & **E\({}_{\text{gap}}\), eV** & **p, Bohr3** & \(\mu\), Debye** & \(\chi\)**, eV** & \(\eta\), eV** & \(\Delta\)**N** \\ \hline EEA4 NB & \(-9.41\) & \(-1.2\) & 8.21 & 221.57 & 16.715 & 6.033 & 2.9449 & 0.164 \\ \hline anion & \(-8.591\) & \(-1.093\) & 7.498 & 148.04 & 11.753 & 4.794 & 1.798 & 0.613 \\ \hline cation & \(-10.695\) & 0.992 & 11.687 & 69.9 & 4.225 & 5.039 & 3.801 & 0.258 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The calculated quantum chemical parameters of the studied inhibitors. increased adsorption on the metal surface. Consequently, it enhances corrosion inhibition efficiency when compared to EEA4 NB and the cation, respectively. Literature reports indicate that the fraction of electrons transferred from the inhibitor to the metallic surface (\(\Delta\)N, Table 4) reflects the inhibition effect resulting from electron donation [27; 28]. A positive \(\Delta\)N value indicates that the molecules function as electron donors, and the inhibition efficiency increases with higher \(\Delta\)N values. It was observed that the anion has the highest fraction of electrons transferred compared to EEA4 NB and the cation. The active sites of the inhibitor molecule can also be described by Fukui functions and dual descriptors, which are associated with sites of nucleophilic and electrophilic  
Figure 6: HOMO and LUMO for the studied inhibitors. Figure 7: Labelling of atoms in the EEA4 NB; grey—carbon, red—oxygen, blue—nitrogen. attacks [29; 30]. The condensed dual descriptors (\(\Delta\)f), combining two Fukui functions, were calculated for each atom using Hirshfeld population analysis [33]. The obtained results are presented in Table 4:  
\[\Delta\text{f}=2\text{q}^{\text{N}}-\text{q}^{\text{N+1}}-\text{q}^{\text{N-1}} \tag{7}\]  
where \(\text{q}^{\text{N}}\), \(\text{q}^{\text{N+1}}\), and \(\text{q}^{\text{N-1}}\) represent the atomic charges for three electronic states with N, N + 1, and N - 1 electrons, respectively. The condensed dual descriptor has a positive value where it is electrophilic and a negative value where it is nucleophilic. However, it is sufficient to determine only which sites have more positive or more negative \(\Delta\)f. If the distribution of \(\Delta\)f around a site A is more positive than another site B, then one can infer that A is a more favorable site for nucleophilic attack than B, while B is a more preferential site for electrophilic attack than A. Each inhibitor molecule was allowed to interact with the metal surface at the atom that has the highest \(\Delta\)f. For both EEA4 NB and the anion, all oxygen atoms were identified as such sites, and for the cation, it was atom O20. However, it is noteworthy that the anion contains both electrophilic and nucleophilic attacking sites. The molecular electrostatic potential (MEP) plot illustrates the molecular size, shape, and regions of positive, negative, and neutral electrostatic potential for EEA4 NB, anion, and cation, with color grading (Figure 8). In the MEP, the maximum negative region, signifying the preferred site for electrophilic attack, is depicted in red, while the maximum positive region, indicating the preferred site for nucleophilic attack, is represented in blue. The potential increases in the order: red < orange < yellow < green < blue. Examining the MEP of the title inhibitors, it is observed that the most negative potential is located over the oxygen atoms of the anion, while the most positive potential is over the cation.