  We have performed first-principles calculations of electronic and dielectric
properties of single-layer bismuth (bismuthene) adsorbed with -COOH. We show
that the Bi-COOH hybrid structure is a two-dimensional topological insulator
with protected edge Dirac states. The adsorption process of -COOH induces a
planar configuration to the initially pristine buckled bismuthene. We claim
that the stability of these planar structure mainly stem from strain induced by
the adsorption of the -COOH organic group, but it is also related to
ligand-ligand interactions. Using charge density analysis we show that the role
of this organic group is not only to stabilize the layer but also to
functionalize it, which is very important for future applications such as
sensing, biomolecules immobilization, as well in electronic spintronic and even
optical devices, due to its large band gap. Finally we demonstrate that many
body corrections are crucial to obtain a better description of the electronic
and dielectric properties of these systems.
