  We theoretically investigate the energy of the ground state exciton confined
to two-dimensional (2D) monolayers with circular shape. Within an effective
mass approach employing a nonlocal screening effect on the Coulomb potential
energy, we demonstrate how the exciton energy is correlated with the radius of
the circle, electron-hole reduced mass, and 2D susceptibility. In addition, we
show that a dead layer around the circle edge, into which the electron-hole
pair cannot penetrate, is necessary for understanding the energy shift recently
observed in monolayer WSe2 quantum dots.
