Tetramerisation of a frustrated spin-1/2 chain
  We investigate a model of a frustrated spin-1/2 Heisenberg chain coupled to adiabatic phonons with a general form of magnetoelastic coupling. For large enough frustration and lattice coupling a new tetramerised phase with three different bond lengths is found. We argue that the zig-zag spin-1/2 chain LiV$_2$O$_5$ might be a good candidate to observe such a phase. 
Federico Becca, Frederic Mila, and Didier Poilblanc