Impurity effects on the electronic structure and spectra of spherical quantum dots by the 4-component relativistic coupled cluster method

Few-electrons quantum dots, confined by 3-dimensional isotropic harmonic potentials, with impurities that mimic finite-size atomic nuclei, are studied. The Dirac-Coulomb Hamiltonian serves as framework, so that relativistic effects are included, and electron correlation is treated at a high level by the multireference Fock-space coupled cluster method, with single and double excitations summed to all orders. Large basis sets composed of Cartesian Gaussian functions are used. Energies of ground and excited states are calculated. Relativistic effects are negligible for low strengths of the harmonic potential ω and small impurity charge Z, and increase rapidly for stronger potentials. Breit contributions, coming from the lowest-order relativistic correction to the interelectronic repulsion, are also studied. The relative weight of the correlation correction is significant for these systems, in particular for small systems with weak confining potentials and low impurity charges Z, where it constitutes up to 17% of the total energy. Strong non-additivity is observed for some low values of Z and ω, where correlation increases with Z and ω, opposite to the effect of each of these potentials separately. A suggestion is made to investigate quantum dots with impurities off the dot center.