We have defined the correlated function as
ΨC=∏i<jg(rij)=N∏i<jg(rij)=N∏i=1N∏j=i+1g(rij),with rij=|ri−rj|=√(xi−xj)2+(yi−yj)2+(zi−zj)2 in three dimensions or rij=|ri−rj|=√(xi−xj)2+(yi−yj)2 if we work with two-dimensional systems.
In our particular case we have
ΨC=∏i<jg(rij)=exp{∑i<jf(rij)}.