  Confined geometries such as semiconductor quantum dots are promising
candidates for fabricating quantum computing devices. When several quantum dots
are in proximity, spatial correlation between electrons in the system becomes
significant. In this article, we develop a fully variational action integral
formulation for calculating accurate few-electron wavefunctions in
configuration space, irrespective of potential geometry. To evaluate the
Coulomb integrals with high accuracy, a novel numerical integration method
using multiple Gauss quadratures is proposed. Using this approach, we
investigate the confinement of two electrons in double quantum dots, and
evaluate the spatial entanglement. We investigate the dependence of spatial
entanglement on various geometrical parameters. We derive the two-particle
wavefunctions in the asymptotic limit of the separation distance between
quantum dots, and obtain universal saturation values for the spatial
entanglement. Resonances in the entanglement values due to avoided
level-crossings of states are observed. We also demonstrate the formation of
electron clusters, and show that the entanglement value is a good indicator for
the formation of such clusters. Further, we show that a precise tuning of the
entanglement values is feasible with applied external electric fields.
