Abstract As self-consistent LDF-DVM method is used to study the chemisorption of I/Si(lll) and I/Ge(lll). Two cluster models are adopted to simulate the top site and 3-fold site respectively. The optimum geometry is determined by minimizing the total energy. Chemisorption of iodine on top site is found to be more stable than that on 3-fold site. The results are in good agreement with the of SEXAFS. A series of DOS are calculated for the chemisorption of column VII elements F, Cl, Br, I on the top site of Si(lll) surface. The results are analysed and compared with experiments and other theories. In addition, the applicability and limitations of semi-empirical method EHT are discussed.