The cluster model has been widely used to study the local structures and physical or chemical properties of minerals. When used to calculate the equilibrium stable isotope fractionation, one question should be considered, i. e. , whether the translational and rotational energies in the Urey model can be excluded? This study provides a detailed theoretical & computational evaluation on their contribution to the reduced partition function ratio (RPFR). The authors suggested that the translational and rotational contributions should not be neglected for the isotope fractionation calculation.