Amount of CO₂ ice during ice warm-up for a H₂O:CO₂ 5:1 ice 20 ML thick simulated by different models: the implemented three-phase model described here (black solid line), the original three-phase model by Hasegawa & Herbst (1993) (green dashed line), the Viti et al. (2004) model (blue dash-dotted line). A heating rate of 1 K per century is used in the two first models and desorption around a 5 solar masses protostar is presented from the Viti et al. (2004) model case.