By combining model-potential molecular dynamics simulations and ab initio calculations, the microscopic mechanism of Si trapping by C substitutional defects (CS) was investigated. It was found that, upon Si trapping, C was converted into an interstitial mobile complex (CI) by an efficient exothermic reaction. Interstitial carbon CI may further interact either with another CS, forming the well-known CICS dicarbon complex, or with extra Si and C interstitials. In particular, two structures, CII and CICI, were identified and characterized. They were found energetically stable so that they could play a crucial role in the process of C aggregation. According to the calculations, CICI may be formed by the interaction of one I with a CICS, proving that the latter was not a deactivated trap for interstitials. The results further suggested that CII and CICI were seeds for further C aggregationSelf-Interstitial Trapping by Carbon Complexes in Crystalline Silicon. A.Mattoni, F.Bernardini, L.Colombo: Physical Review B, 2002, 66[19], 195214 (6pp)