Calculation of hyperfine splitting in mesons using configuration   interaction approach
  The spin - spin mass splitting of light, heavy and mixed mesons are described within a good accuracy in the potential model with screened potential. We conclude that the long - distance part of the potential cannot be pure scalar and that a vector - scalar mixture is favoured. With the same parameters which gives correct average mass spectrum excellent spin - spin splittings of heavy quarkonia is obtained. The results are obtained by going beyond usually used perturbation method, namely using configuration interaction approach. 
V. Lengyel, Yu. Fekete, I. Haysak, A. Shpenik