  Using first-principles calculations, we found the topological phase
transition induced by electric fields in one-bilayer Bi(111). The bandgap
decreased with increasing electric field strength, and it is closed at 2.1
V/{\AA}. For fields exceeding 2.1 V/{\AA}, the bandgap increased with
increasing electric field strength, reaching 0.34 eV at 4.0 V/{\AA}. We
computed the $Z_{2}$ invariant that characterizes topological insulator phases.
As results, one-bilayer Bi(111) showed a topological phase transition induced
by the electric field, from the topological insulator phase to the trivial
insulator phase through a Dirac semimetal. This topological phase transition
could be applied to novel devices.
