  The ground-state wave function and the energy gap are calculated for various
layer separations d and for up to 24 electrons by the density matrix
renormalization group (DMRG) method. Two-particle distribution function and
excitonic correlation function are calculated from the ground-state wave
function, and the evolution of the ground state with increasing d is analyzed.
The results indicate that the transition is continuous. A smooth crossover of
the ground state is found at around d/l ~ 1.6 from the excitonic character at
small d/l to the independent Fermi-liquid character at large d/l, where l is
the magnetic length.
