Neutral anion energy differences for a large class of a.-substituted silyl radicals have been computed to determine the effect of alkyl, silyl, and halo substituents on their electron affinities. In particular, we report theoretical predictions of the adiabatic electron affinities (AEAs), vertical electron affinities (VEAs), and vertical detachment energies (VDEs) for a series of methyl-, silyl-, and halo-substituted silyl radical compounds. This work utilizes the carefully calibrated DZP++ basis set (Chatgilialoglu, C. Chem. Rev. 2002, 102, 231), in conjunction with the pure BLYP and OLYP functionals, as well as with the hybrid B3LYP, BHLYP, PBE1PBE, MPW1K, and O3LYP functionals. Bromine has the largest effect in stabilizing the anions, and the BLYP/DZP++ AEA for SiBr3 is 3.29 eV. The other predicted electron affinities are for SiH3 (1.37 eV), SiH2CH3 (1.09 eV), SiH2F (1.54 eV), SiH2Cl (1.94 eV), SiH2Br (2.05 eV), SiH2(SiH3) (1.77 eV), SiH(CH3)(2) (0.92 eV), SiHF2 (1.86 eV), SiHCl2 (2.53 eV), SiHBr2 (2.67 eV), Si(CH3)(3) (0.86 eV), SiF3 (2.66 eV), SiCl3 (3.21 eV), Si(SiH3)(3) (2.25 eV), and SiFClBr (3.13 eV). For the five silyl radicals where experimental data are available, the BLYP functional gives the most accurate determination of AEAs; the average absolute error is 0.04, eV, whereas the corresponding errors for the O3LYP, MPW1K, PBE1PBE, B3LYP, OLYP, and BHLYP functionals are 0.05(8), 0.06(0) 0.06(3), 0.08(5), 0.11(5), and 0.15(3) eV, respectively.