Fig. 3 Top and side view of a) single vacancy defective silicene and b) Stone-Wales defective silicene
The single vacancy leads to an increase in the otherwise uniform Si-Si bond lengths from 2.27 Å to 2.34 Å near the proximity of the defect. This change in the Si-Si bond length is also observed in the Stone-Wales defective system which relaxes into two seven-membered rings with two surrounding five-membered rings. The Si-Si bond adjoining the two seven membered rings was measured to be 2.17 Å while the average Si-Si bond adjoining the seven membered ring to the five and six membered rings was seen to measure 2.32 Å. The decrease in the bond length between the Si atoms adjoining the seven membered rings can be attributed to the increased electron distribution near the rotated Si-Si bond which leads to a stronger bond. The defect formation energies for the two systems were calculated using Equation (1) and it was seen that the Stone-Wales defect is more likely to form with a lower defect formation energy of 2.10 eV compared to that of the single vacancy defect which was measured as 3.35 eV. These defect formation energies were found to be much lower than the ones found in graphene as in seen in Fig S1 in the supplementary information which increases their prevalence during manufacturing, thus leading to more sites where H2molecules can be stored. This is caused primarily due to the larger size of the Si atom causing lower Π-Π overlap between the Si atoms, which leads to weaker bonds compared to the C-C bonds in graphene [53]. The density of states (DOS) for the defective systems were also plotted and can be seen in the supplementary information in Fig. S2. All the structure parameters and formation energies were found to be in good agreement with previous studies and these structures were used for further calculations [54, 55].

3.2 Lithium Decoration on Pristine and Defective Silicene