S1plus(x) * S2minus(x) + S1minus(x) * S2plus(x) S2minus(x) *S1plus(y) + S2plus(x) *S1minus(y) (S2minus(x)*(1/2-S1z(y))*S2plus(y) + S2plus(x)*(1/2-S1z(y))*S2minus(y) +S1minus(x)*(1/2-S2z(x))*S1plus(y) + S1plus(x)*(1/2-S2z(x))*S1minus(y)) -h*Sz(i) + Jz*S1z(i)*S2z(i) +Jxy*exchange_site(i) Jz*S2z(i)*S1z(j)+0* Jxy *exchange_xy(i,j) + tcor *hop_cor(i,j)