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\bibitem{Riva_etal2004} {\textquotedblleft}\textit{Neutral and charged donor in a 3D quantum dot}{\textquotedblright}. Riva C, Escorcia R, Peeters FM, Physica. E: Low-dimensional systems and nanostructures \textbf{22}, 550 (2004).   http://doi.org/10.1016/j.physe.2003.12.067

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