  A new approximate scheme, DSUB$m$, is described for the coupled cluster
method. We then apply it to two well-studied (spin-1/2 Heisenberg
antiferromagnet) spin-lattice models, namely: the $XXZ$ and the $XY$ models on
the square lattice in two dimensions. Results are obtained in each case for the
ground-state energy, the sublattice magnetization and the quantum critical
point. They are in good agreement with those from such alternative methods as
spin-wave theory, series expansions, quantum Monte Carlo methods and those from
the CCM using the LSUB$m$ scheme.
