Spin Spin correlation for 2 leg isotropic heisenberg model

[shuklavaibhav]

I was trying to reproduce the known results of the said model, and I have attached my results along with the known results. I have also pasted my snippet for correlations, which worked perfectly for a 1D system with periodic and open boundaries, but is not working for ladder systems. I need some help.
Thank you for your attention.
I can give my codes for Hamiltonian, DMRG, and anything else if needed

for r in 0:(L ÷ 2)
    total = 0.0

   

    for j in 1:N
        x   = (j - 1) % L + 1
        leg = (j - 1) ÷ L
        xp  = (x + r - 1) % L + 1
        i   = leg*L + xp
       
       os = OpSum()
        os += 1.0, "Sz", j, "Sz", i
        os += 0.5, "S+", j, "S-", i
        os += 0.5, "S-", j, "S+", i
        Hij = MPO(os, sites)
        val = real(inner(psi, Apply(Hij, psi)))


        total += val 
    end

    
    cor[r+1] = real(((-1)^r * total) / (2L))
    
end