Two adducts SF 4 ·AsF 5 and SF 4 ·SbF 5 have been studied in this work. Their structures, thermodynamic functions, and heats of formation were studied using density functional theory (DFT) method in gas phase and using the force field method and the DFT GGA-RPBE method in crystal state. The obtained crystal structures have the P2 1 /c space group. The lattice energies, sublimation enthalpies and heats of formation in crystal state were estimated. Based on the optimized crystal structures, the electronic energy band and density of state were predicted and the results indicate that they are semiconductors with the band gap between 2.3 ～ 2.5 eV.