  We present an atomistic model for predicting the distribution of doping
electric charges in layered molybdenum disulfide (MoS$_{2}$). This model mimics
the charge around each ion as a net Gaussian-spatially-distributed charge plus
an induced dipole, and is able to predict the distribution of doping charges in
layered MoS$_{2}$ in a self-consistent scheme. The profiles of doping charges
in monolayer MoS$_{2}$ flakes computed by this charge-dipole model are in good
agreement with those obtained by density-functional-theory calculations. Using
this model, we quantitatively predict the charge enhancement effect in
MoS$_{2}$ monolayer nanoribbons, with which strong ionic charge-localization
effects are shown.
