Probability threshold truncation in a symplectic basis for ab initio nuclear structure calculations

The size of bases used in ab initio nuclear structure calculations explodes with the number of nucleons and allowed excitation quanta. Thus, finite computational resources limit the convergence of calculated observables. The symplectic no-core configuration interaction (SpNCCI) framework reorganizes the basis into Sp(3,R) irreducible representations (irreps), allowing us to truncate this basis by symplectic symmetry. Here, we apply a truncation scheme where the basis is truncated based on probability contributions of Sp(3,R) irreps to a reference wavefunction obtained in an initial small-scale calculation. This lets us retain only irreps which dominantly contribute to the wavefunction and incorporate high-lying basis states within these irreps previously unattainable given fixed resource constraints, in attempt to better converge long-range observables such as charge radii and quadrupole moments. We explore the effect of this truncation on convergence of calculated observables and the size of the SpNCCI basis.