A method is developed to obtain the alloy scattering coefficients from first-principles band structure calculations. It is found that the scattering matrix can be decomposed into two additive components: a chemical part due to atomic substitution and a part due to ionic relaxation. The method is then applied to find the intra-and inter-valley electron scattering rates for substitutional carbon in silicon. Intravalley scattering is found to be the dominant process. © 2011 IEEE.