Abstract We have performed self-consistent-field X-alpha scattered-wave (SCF-Xα-SW) calculations on a 13-atom cluster Si4(sat)9 which is used to model the dangling bond defect center in hydrogenated amorphous silicon (a-Si:H). The transition state concept of the SCF-Xα-SW method was applied to the model cluster to determine the effective correlation energ U eff. The effects of local relaxations around the positively (T 3 +) and negatively (T 3 −) charged dangling bond defect centers were examined. The results yield a negative effective correlation energy (−0.214 eV) if complete local relaxations are allowed. Also they indicate a dependence of the value of U eff on the degree of relaxation around the T 3 + and T 3 − centers - both positive and negative values can occur. Implications of these results are discussed.