Molecular dynamics simulations of the devitrification process of a lead fluoride glass doped with Er(3+) ions were carried out. This technique appears to be a relevant way to perform systematic analysis of the system structure and to study the influence of defects on PbF2 crystallization. We modeled the total enthalpy, the radial distribution functions, and the diffracted intensities of systems containing different amounts of Er(3+) ions. We demonstrated by means of different simulations that Er(3+) ions lowered the devitrification temperature of PbF2, in good agreement with the experimental results. The genuine role of Er(3+) ions in the devitrification process of PbF2 has been investigated. Er(3+) ions have an unquestionable influence of the crystallization of PbF2. Although the latter does not start in the nearest neighborhood of Er(3+) ions, the presence of Er(3+) ions in a close environment may favor the lead fluoride crystallization.