Theoretical study. The theoretical study involved calculations using software programs from Accelrys. Density functional theory code DMol3 was applied to calculate energy, geometry, and frequencies implemented in Materials Studio 5.5 .
We employed the double numerical polarized basis set that includes all the occupied atomic orbitals plus a second set of valence atomic orbitals, and polarized d-valence orbitals, and correlation generalized gradient approximation was applied in the manner suggested by these are the conditions for the highest-accuracy level in DMol3. The spin unrestricted approach was exploited with all electrons considered explicitly. The real space cutoff of 5 A was imposed for numerical integration of the Hamiltonian matrix elements. The self-consistent field convergence criterion was set to the root-mean-square change in the electronic density to be less than 10-16 electron/A3. The convergence criteria applied during geometry optimization were 2.72*10-4 eV for energy and 0.054 eV/A for force.