Variational calculations in gauge theories with approximate projection   on gauge invariant states
  Variational calculations using Gaussian wave functionals combined with an approximate projection on gauge invariant states are presented. We find that the energy exhibits a minimum for a wave functional centered around a non vanishing background magnetic field. We show that divergences can be removed by a renormalization of the coupling constant. The resulting expectation value of the gluon condensate is found to be in qualitative agreement with phenomenological estimates. 
C. Heineman, C. Martin, D. Vautherin and E. Iancu