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