Periodic Anderson model with d-f interaction
  We investigate an extended version of the periodic Anderson model where an interaction is switched on between the doubly occupied d- and f-sites. We perform variational calculations using the Gutzwiller trial wave function. We calculate the f-level occupancy as a function of the f-level energy with different interaction strengths. It is shown that the region of valence transition is sharpened due to the new interaction. 
I. Hagymasi, K. Itai, J. Solyom
cond-mat.str-el