  We study the formation of molecular states in a two-electron quantum dot as a
function of the barrier potential dividing the dot. The increasing barrier
potential drives the two electron system from an artificial helium atom to an
artificial hydrogen molecule. To study this strongly coupled regime, we
introduce variational wavefunctions which describe accurately two electrons in
a single dot, and then study their mixing induced by the barrier. The evolution
of the singlet-triplet gap with the barrier potential and with an external
magnetic field is analyzed.
