In this paper, we report the calculation of the enthalpy of sublimation, Delta H-sub, as a function of temperature of crystalline beta-cellobiose from molecular dynamics (MD) simulations, using two popular carbohydrate force fields. Together with the entropy difference between the solid and the vapor, AS, evaluated at atmospheric pressure, Delta H-sub gives the vapor pressure of cellobiose over the solid phase as a function of T. It is found that when quantum mechanical corrections to the enthalpy calculated from the distribution of normal modes is applied both force fields give Delta H-sub close to experiments. The entropy change, Delta S, which is calculated within a harmonic approximation becomes too small, leading to vapor pressures that are too low. These findings are relevant to MD simulations of crystalline carbohydrates in general, e.g., native cellulose.