3.2.1 Monte Carlo simulations
It is of imperative in quantifying the various energetic outputs, to know the preferential adsorption and orientation of the adopted additives on the alloy surface.45 The energy values (in term of different contributions) during the random MC configuration search are shown in Figure 3 . From this figure 3, the total average energy reached the equilibrium at after 3000000 MC suggesting that additives reached the low energy stable arrangement. The interaction of the OPD & PPD onto the Ni-W surface gives a mean to evaluate the required energies for this adsorption. The quantitative adsorption energy (Eads) is calculated by using equation 2:25,27,46,47
\begin{equation} E_{\text{adsorption}}=E_{\text{Ni}-W\left(110\right)\text{CPQ}\ \text{orMPQ}\text{\ \ \ }}-\left({\text{Ni}-W}_{\left(110\right)}+E_{\text{OPD}\ \text{or}\text{\ \ }\text{PPD}}\right)\text{\ \ \ .\ \ .\ \ .\ \ \ }\text{Equation}\ 2\nonumber \\ \end{equation}
where\(\text{Ni}-W\left(110\right)\text{OPD}\ \text{or}\ \text{PPD}\)is the total energy of the simulated corrosion system, ENi-W, and EOPD or PPD is the total energy of the Ni-W(110) surface and free inhibitor.
The most stable or the low energy adsorption sites of organic additives (OPD & PPD) in the vicinity of Ni-W alloy surface and corresponding adsorption energetic outputs (Eads) obtained via a huge number of randomly configurations from Monte Carlo calculations were figured out in Figure 4. It is of significant in knowing the adsorption energy (Eads) which denotes to the sum of deformation energy and rigid adsorption energy of additive components.48Additionally, Eads corresponds to the release of energy, while the organic additives (OPD&PPD) relaxed on the surface of alloy. The Max.adsorption energy distribution was found to be −121.25 kcal/mol and −195.55 kcal/mol for OPD & PPD additive molecules respectively. A noticeable larger negative value of Eads = −195.55 kcal/mol (PPD) infers that the adsorbed organic layer on the alloy surface is spontaneous and more stable,49 then the earlier molecular layer (OPD). Moreover, this higher negative value (Eads = −195.55 kcal/mol) evidence the fact that mere amount of energy is required for the PPD molecule for adsorption onto the Ni-W alloy surface45 intensifying the surface coverage area, thus providing a durable shield against corrosive suppressing agents.50