  We present an all-electron calculation of the hyperfine parameters for
conduction electrons in Si, showing that: (i) all parameters scale linearly
with the spin density at a $^{29}$Si site; (ii) the isotropic term is over 30
times larger than the anisotropic part; (iii) conduction electron charge
density at a Si nucleus is consistent with experimental estimates; (iv)
Overhauser fields in natural Si quantum dots (QDs) are two orders of magnitude
smaller than in GaAs QDs. This reinforces the outstanding performance of Si in
keeping spin coherence and opens access to reliable quantitative information
aiming at spintronic applications.
