Microscopic model for the novel frustrated Cu(II)-spin tetrahedron-based   Cu4Te5O12X4 (X=Cl, Br) systems
  We present a microscopic study of the electronic and magnetic properties of the newly synthesized Cu(II)-spin tetrahedron-based Cu4Te5O12Cl4 compound based on Density Functional calculations and on ab initio-derived effective models. In view of these results, we discuss the origin of the observed differences in behavior between this system and the structurally similar and much studied Cu2Te2O5Cl2. Since the Br analog of the title compound has not been synthesized yet, we derive the crystal structure of Cu4Te5O12Br4 by geometry optimization in an ab initio molecular dynamics calculation and investigate the effect of substituting Cl by Br as well as the possible magnetic behavior of this system and compare with the recently studied sister compound, Cu2Te2O5Br2. 
Badiur Rahaman, Harald O. Jeschke, Roser Valenti and T. Saha-Dasgupta