## 3 Results and Discussion
### Na-Dominant Clinoptilolite
#### 3.1.3 Interaction of Na Cations with the Framework  
Figure 6 shows the most stable configuration for the Na-dominant clinoptiolite. The distance between two Na atoms in 10 MR of channel A increased to ~6.26 A from the previous value of ~4.67 A, the maximum possible distance between the two Na atoms in such a structure. After optimization, they approached the sides of the channels or converged to the corners of the channel to compensate for the negative charge induced by the presence of Al at T2, denoted as 'Al2' in the figure, thus positioning themselves at distances of ~3.30 A and ~3.47 A on the left and right sides of the channel, respectively. The reasons for this Na-Na distance are three-fold. On the one hand, the two Na atoms aim to stabilize the negative framework charge enveloping the two Al atoms positioned at the left and right extremities of the channel. While this could be achieved by Na2 in the 8 MR of channel B on the left side of the channel, it was carried out by Na1 for the Al2 on the left side. It is an energetically more favorable process for Na1 at the left side of the channel moves to stabilize the framework oxygens rather than Na2 in channel B since the Na1 was closer than Na2. It is worth mentioning that the left, right, up, and down movements of cations mentioned in this study are relative to the projections of the corresponding figures.  
Furthermore, the presence of Al1 disrupts the Na atoms, preventing them from bonding with any framework oxygens that are in close proximity to Al1. Therefore, the Na1 at the right side of the channel shifted upward, thereby increasing its distance from Al1 from 5.39 A to 5.86 A, which inherently led to an increase in the distance to the other Na atom. The third reason for the significant distance between Na atoms is attributed to the absence of water molecules. When dehydrated, cations tend to relocate to sites that have increased framework-cations interactions. This leads to shorter distances between the framework oxygen and the extra-framework cations. Moreover, there is a local charge dissatisfaction for the exposed positive portion of these movable cations. As [PERSON] stated, each ion should approach an electrostatically balanced environment, which was not satisfied in this case. An identical scenario occurred for Al2 situated at the upper right of the structure, where Na2 in the 8 MR of channel B moved, rather than Na1, to bond with the framework oxygens, as Na2 is positioned closer to Al2 than Na1. This reduces the distance between Al2  
Figure 6: (**a**) The most stable configuration in the c-direction, illustrating the displacement of the extra-framework cations following optimization, and (**b**) the same configuration before optimization.  
and Na2 from \(\sim\)3.27 A to \(\sim\)3.13 A. For Al3 at the upper left part of the structure in Figure 6, again, the Na1 moved to bond with the oxygen surrounding Al3 and does not approach the oxygen surrounding Al1 at the lower left part of the cell, leading to a distance of \(\sim\)3.27 A between Al3 and Na1, which was \(\sim\)3.53 A. A discussion of the least stable configuration can be found in the Supplementary Material.