  Ground-state energy is exactly calculated for the spin-1/2 Heisenberg-Ising
bond alternating chain with the Dzyaloshinskii-Moriya interaction. Under
certain condition, which relates a strength of the Ising, Heisenberg and
Dzyaloshinskii-Moriya interactions, the ground-state energy exhibits an
interesting nonanalytic behavior accompanied with a gapless excitation
spectrum.
