Ab initio calculation of electromagnetic observables in the p-shell using translationally-invariant intrinsic operators

Ab initio methods in nuclear theory strive to make quantitative predictions of nuclear observables, starting with the internucleon interaction. In the no-core configuration interaction (NCCI) approach, calculations have traditionally been performed with harmonic oscillator functions and N_max truncation due the factorizability into center-of-mass and intrinsic wave functions. Use of other bases and truncations (which may have, e.g., better asymptotics or convergence behavior) induces a mixing between these degrees of freedom which contaminates observables calculated using one-body operators. By using translationally-invariant two-body operators in place of their one-body counterparts, we compute electromagnetic observables in the p-shell using other single-particle orbitals, such as natural orbitals, and many-body truncation schemes.