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The obtained data may be related to other aromatic systems, especially those purine-based like adenine and guanine. Such maps would appear to be a guide for qualitative predictions of binding interactions. Accurate multidimensional PES maps, as opposed to the data based only on a small group of systems, could find a vast range of applications in chemistry. Unlike analyzing simple potential energy curves, one could see a broader picture of what occurs and learn how the purine dimer stability changes along with various geometrical parameters. Accurate PES maps of a purine system would enhance the knowledge of the complete understanding of the stacking interaction of this biologically fundamental structural unit. Because of the above, as the focus of this study, the extensive analysis of potential energy surfaces (PES) of model purine–purine dimers, combined with orbital and structural analysis, has been selected. Then, the most stable and populated structures were fully reoptimized at the correlated ab initio level. In some studies, however, the potential energy surfaces have been examined by the molecular dynamics/quenching technique. The study of potential energy surfaces has been limited to learning potential energy curves showing dependencies of the system energy on twist or displacement. The performed studies have mostly focused on analyzing the stationary geometries. The most studied systems are those found in nucleic acids, i.e., adenine and guanine. As for more complex N-heterocycles, like purines, such rigorous studies, to the author’s knowledge, have not been performed. It has become evident that the exploration of NCI landscapes may provide a new insight into NCI in aromatic systems. By using this approach, many vital conclusions have been deduced. Recently, NCI between homodimers of selected heterocycles (pyrrole, furan, thiophene, pyridine, pyridazine, pyrimidine and pyrazine) have been studied to explore their interaction energy surfaces employing the Möller–Plesset second-order perturbation theory, coupled with small Gaussian basis sets (6-31G* and 6-31G**) with specifically tuned polarization exponents. The same has been done for a pyrrole dimer and, with some limits, to other simple aromatic N-heterocycles (e.g., pyrazine, pyrimidine, pyridazine) with benzene. What is more, to enable a better understanding of the role of the molecular geometrical dependencies on the intermolecular interaction of the stacked pyridine dimer, the accurate potential energy maps of it, based on several geometrical parameters, have been calculated.

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In most cases, the studies have focused on the determination of system energy as a function of selected geometrical parameters, though some other approaches, as full geometry optimizations starting from various unsymmetrical initial dimer arrangements, have also been applied. Since a pyridine dimer is a prototypical example of π– π stacking in N-heterocyclic systems (as benzene dimer is an example of π– π stacking in general), it has been a subject of rigorous theoretical studies. The knowledge can benefit scientists who project and build new crystal systems as well as to those who analyze them. Because of that, there is no doubt that for it to be fully understood, it is necessary to know intermolecular interactions to the highest possible extent. Crystal engineering is based on the knowledge of intermolecular interactions. Though the study of stacking interaction has mostly focused on systems containing benzene rings, the number of such studies on heterocyclic ring systems has been quickly increasing. Hence, N-heterocycles are useful recognition elements in many biological systems, and they are becoming a crucial component in most known drug molecules. N hydrogen bonds), which is often a key to their function.Due to this, they can participate in different interaction patterns (e.g., π-stacking and C–H Such systems, because of the presence of a nitrogen atom in their ring frameworks, are more abundant with π-electrons. All the above strongly refers to N–heterocyclic compounds. They are engaged in a vast array of supramolecular architectures playing a critical role in many chemistry-related fields such as the structures of biomolecules, molecular recognition, the reactivity of molecules, nanoengineering and in crystal engineering concerning systems being a collection of a discrete number of chemical units. Noncovalent interactions (NCI hereafter) involving aromatic rings are pivotal in many areas of science.