Nature of the spin-singlet ground state in CaCuGe2O6
  We investigate by means of ab initio electronic structure analysis and Quantum Monte Carlo calculations the scenario where longer-ranged magnetic interactions dominate over short-ranged interactions in the physical description of compounds. This question is discussed, in particular, for the case of CaCuGe$_2$O$_6$ which shows a spin-singlet behavior induced by third nearest neighbor copper pairs. 
Roser Valenti (1), T. Saha-Dasgupta (2), and Claudius Gros (1) ((1)   University des Saarlandes, Theor. Physics, Germany, (2...