Geometric Global Quantum Discord of Two-qubit States
  We consider the geometric global quantum discord (GGQD) of two-qubit systems. By analyzing the symmetry of geometric global quantum discord we give an approach for deriving analytical formulae of the extremum problem which lies at the core of computing the GGQD for arbitrary two-qubit states. Furthermore, formulae of GGQD of arbitrary two-qubit states and some concrete examples are presented. 
Yunlong Xiao, Tao Li, Shao-Ming Fei, Naihuan Jing, Xianqing Li-Jost   and Zhi-Xi Wang
quant-ph