# Spin Spin correlation for 2 leg isotropic heisenberg model

**URL:** <https://itensor.discourse.group/t/spin-spin-correlation-for-2-leg-isotropic-heisenberg-model/2565>\
**Category:** DMRG and Numerical Methods\
**Created:** [January 16, 2026, 7:03am UTC](https://itensor.discourse.group/t/spin-spin-correlation-for-2-leg-isotropic-heisenberg-model/2565 "2026-01-16T07:03:51Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![shuklavaibhav](https://avatars.discourse-cdn.com/v4/letter/s/ce73a5/32.png) [@shuklavaibhav](https://itensor.discourse.group/u/shuklavaibhav)\
**Post date:** [January 16, 2026, 7:03am UTC](https://itensor.discourse.group/t/spin-spin-correlation-for-2-leg-isotropic-heisenberg-model/2565/1 "2026-01-16T07:03:51Z")

</div>

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

```cor

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

```

 ![image](https://global.discourse-cdn.com/free1/uploads/itensor/original/1X/7647e973f75a75febc63f3bdecc1df6cb2fd1deb.png) ![image](https://global.discourse-cdn.com/free1/uploads/itensor/original/1X/df27b517173f8e3e5d3c261d280185ef608e5161.png)