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260 PublicacionesJ. L. MOVILLA AND J. PLANELLES PHYSICAL REVIEW B 74, 125322 2006tion induced by the dielectric discontinuity strongly affectsinterparticle correlations and interaction energies. In addition,the study also demonstrates how the combination ofsingle- and two-particle Coulombic effects may give rise, inweakly confined D − systems, to the appearance of differentphases. Strong, Wigner-like localizations of the electronicdensity and important reconstructions of the two-electronground state are found.The main conclusions of the paper are itemized as follows.i Surface states in QDs surrounded by air or a vacuummay localize the electronic density in the external medium,and, then, electrons undergo a strong angular correlation.This correlation is gradually reduced as the QD dielectricconstant increases, due to the influence of the polarizationcharges induced at the dielectric interface.ii In the case of surface states in air-filled nanocavitiesof semiconductor matrices, polarization charges reduce theelectronic correlation to a greater extent than in the QD case.iii A transition phase from volume to surface states accompaniedby a strong radial Wigner-like localization of theelectronic density is produced when a quantum dot is dopedwith a central shallow donor impurity in the weak confinementregime. Within this phase, the D − center presents zerobinding energy, providing a situation in which the systembehaves as a twofold electron reservoir. We show that theimpurity is able to attach the first excess electron strongly.However, this electron totally blocks the effect of the impurity,and the system now behaves as an undoped and emptyQD for the second excess electron.iv The radial-Wigner phase vanishes as we approach thestrong confinement regime. However, it is stable within awide range of QD sizes, thus making its experimental searchand characterization feasible.ACKNOWLEDGMENTSFinancial support from MEC-DGI Project No. CTQ2004-02315/BQU and UJI-Bancaixa Project No. P1-B2002-01Spain is gratefully acknowledged. A Spanish MECD FPUgrant is also acknowledged J.L.M..*Electronic address: planelle@exp.uji.es1 L. Bányai and S. W. Koch, Semiconductor Quantum Dots WorldScientific, Singapore, 1993.2 L. E. Brus, J. Chem. Phys. 80, 4403 1984.3 V. A. Fonoberov, E. P. Pokatilov, and A. A. 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For example, the interaction betweentwo electrons in a completely uniform medium so that nopolarization terms coming from dielectric mismatches arisewith permittivity 1 is given by the bare Coulomb term e 2 /r.125322-8