Dilute Cu-based alloys containing S, P, and Ag impurities and also vacancies are studied theor- etically on the basis of total energy calculations. This is done within the supercell approach by using the locally self consistent Green's function (LSGF) method. The impurity solution energies, volume misfits, and interaction energies for these defects are calculated and used to study the microscopic mechanism behind the effect of these impurities on embrittlement of copper at intermediate temperatures. It is shown that the solubility of S in Cu is low due to precipitation of the highly stable Cu_2S phase. A large binding energy of a sulfur-vacancy defect pair in the first coordination shell (-0.46 eV) and a sulfur-sulfur defect pair in the second coordination shell (-0.12 eV) seem to favor this precipitation. The effect of phosphorus and silver impurities on the bulk S solubility has also been studied, and was found to depend on the com- petition of these impurities with sulfur for vracancies, as well as probably for other lattice defects.
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