Аннотация:In recent years, remarkable progress has been achieved in developing novel non-perturbative techniques for constructing valence space shell model Hamiltonians from realistic internucleon interactions. One of these methods is based on the Okubo–Lee–Suzuki (OLS) unitary transformation applied to no-core shell model (NCSM) solutions. In the present work, we implement the corresponding approach to solve for valence space effective electromagnetic operators. To this end, we use the NCSM results for A = 16−18, obtained at Nmax = 4, to derive a charge-dependent version of the effective interaction for the sd shell, which allows us to exactly reproduce selected NCSM spectra of 18O, 18F and 18Ne within the two valence nucleon space. We then deduce effective single-particle matrix elements of electric quadrupole (E2) and magnetic dipole (M1) operators by matching them to the electromagnetic transi- tions and moments for 17O and 17F from the NCSM at Nmax = 4. Thus, effective E2 and M1 operators are obtained as sets of single-particle matrix elements for the valence space (sd shell) which allow us to reproduce the NCSM results for A = 17 exactly. Systematic comparison of a large set of sd shell results on quadrupole and magnetic dipole moments and transitions for A = 18 using effective E2 and M1 operators that we derive from the full NCSM calculations demonstrates a remarkable agreement.