  We demonstrate the possibility of creating domain walls described by a single
component Gross-Pitaevskii equation with attractive interaction, in the
presence of an optical-lattice potential. While it is found that the extended
domain wall is unstable, we show that the external magnetic trap can stabilize
it. Stable solutions include twisted domain walls, as well as asymmetric
solitons. The results also apply to spatial solitons in planar waveguides with
transverse modulation of the refractive index.
