We report on the development of a new theoretical tool that allows for isospin
projection of Slater determinants and we present its
first applications. In particular, we determine
the isospin mixing in ground states of
![$N=Z$](img7.png)
nuclei
and discuss its dependence on the size of the harmonic-oscillator basis
used in the calculations.
We also discuss the unphysical contribution
to the isospin mixing caused by the spurious isospin-symmetry breaking
inherent to the mean-field approach. We show that these contributions may
be as large as 30% of the value of the isospin-mixing parameter.