Exact Groundstates for Antiferromagnetic Spin-One Chains with Nearest   and Next-Nearest Neighbour Interactions
  We have found the exact ground state for a large class of antiferromagnetic spin-one chains with nearest and next-nearest neighbour interactions. The ground state is characterized as a matrix product of local site states and has the properties characteristic of the Haldane scenario. 
C. Lange, A. Kl\"umper, J. Zittartz