Effective Shell-Model interactions from the No-Core Shell-Model*

No-Core shell model calculations (NCSM) for heavier nuclei, partially filling the sd-shell is a challenging problem. This is due to the exponential growth in the dimension of the Hilbert space. It is desirable to find an effective interaction, which utilizes a much smaller model space, that accurately reproduces NCSM results. Core shell-model calculations employ either empirical or theoretical effective 2-body matrix elements (TBME) that neglect the many body-correlations present. We show how a NCSM investigation in a 4$\hbar$$\Omega$ model space can yield effective TBME specific for the sd-shell, which accurately reproduce the many-body correlations present in the original calculation. TBME for $^{18}$F are obtained by direct projection, and their capability to reproduce large scale NCSM calculations is demonstrated for F, Ne and Na isotopes.