  Intercalation (ic) of metal atoms into the van der Waals (vdW) gap of layered
materials constitutes a facile strategy to create new materials whose
properties can be tuned via the concentration of the intercalated atoms. Here
we perform systematic density functional theory calculations to explore various
properties of an emergent class of crystalline 2D materials (ic-2D materials)
comprising vdW homobilayers with native metal atoms on a sublattice of
intercalation sites. From an initial set of 1348 ic-2D materials, generated
from 77 vdW homobilayers, we find 95 structures with good thermodynamic
stability (formation energy within 200 meV/atom of the convex hull). A
significant fraction of the semiconducting host materials are found to undergo
an insulator to metal transition upon self-intercalation with only PdS$_2$,
PdSe$_2$, and GeS$_2$ maintaining a finite electronic gap. In five cases,
self-intercalation introduces magnetism. In general, self-intercalation is
found to promote metallicity and enhance the chemical reactivity on the basal
plane. Based on the calculated H binding energy we find that self-intercalated
SnS$_2$ and Hf$_3$Te$_2$ are promising candidates for hydrogen evolution
catalysis. All the stable ic-2D structures and their calculated properties can
be explored in the open C2DB database.
