  A new constraint of clustering for the AMD calculation is proposed. This new
constraint gives us large improvement in studying the cluster structure by AMD
which sometimes meets difficulty in giving rise to some specific cluster
configurations. The usefulness of this new constraint is verified by applying
it to the the study of the third $K^\pi = 0^+$ band of $^{20}$Ne which has been
discussed to have $2\alpha$-$^{12}$C structure. This band has not been easy
even to construct by AMD. We see that the AMD+GCM calculation by the use of the
new constraint gives rise to the third $K^\pi = 0^+$ band which contains the
$2\alpha$-$^{12}$C structure as an important component.
