  The newly observed ($\sqrt3$$\times$$\sqrt3$) surface reconstruction in
heteroepitaxial Si(111) thin films on metal substrates is widely considered as
a promising platform to realize 2D Dirac and topological states, yet its
formation mechanism and structural stability are poorly understood, leading to
the controversial terminology of "multilayer silicene". Based on valence bond
and conjugation theory, we propose a {\pi}-conjugation plus charge-transfer
model to elucidate such a unique "bamboo hat" surface geometry. The formation
of planar ring-shaped {\pi}-conjugation and charge transfer from the rings to
upper buckled Si atoms greatly lower the surface dangling bond energy. We
justify this unconventional Si structural model by analyzing from
first-principles surface energies and surface stress tensors as a function of
strain. Within the same formalism, additional metastable surface
reconstructions with the similar "bamboo hat" features are predicted which
opens possibilities to other exotic electronic states in silicon.
