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We introduce a new framework for studying clustering and for calculating α partial widths using ab initio wave functions. We demonstrate the formalism for Ne20, by calculating the overlap between the O16+α cluster configuration and states in Ne20 computed in the abinitio symmetry-adapted no-core shell model. We present spectroscopic amplitudes and spectroscopic factors, and compare those to no-core symplectic shell-model results in larger model spaces, to gain insight into the underlying physics that drives α clustering. Specifically, we report on the α partial width of the lowest 1- resonance in Ne20, which is found to be in good agreement with experiment. We also present first no-core shell-model estimates for asymptotic normalization coefficients for the ground state, as well as for the first excited 4+ state in Ne20 that lies in a close proximity to the α+16O threshold. This outcome highlights the importance of correlations for developing cluster structures and for describing α widths. The widths can then be used to calculate α-capture reaction rates for narrow resonances of interest to astrophysics. We explore the reaction rate for the α-capture reaction O16(α,γ)20Ne at astrophysically relevant temperatures and determine its impact on simulated x-ray burst abundances.

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Physical Review C