# How to compute multisite exponential operator for DMRG

**URL:** <https://itensor.discourse.group/t/how-to-compute-multisite-exponential-operator-for-dmrg/825>\
**Category:** DMRG and Numerical Methods\
**Tags:** julia, dmrg, mps, mpo\
**Created:** [April 29, 2023, 6:35pm UTC](https://itensor.discourse.group/t/how-to-compute-multisite-exponential-operator-for-dmrg/825 "2023-04-29T18:35:50Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Aditya214](https://yyz2.discourse-cdn.com/free1/user_avatar/itensor.discourse.group/aditya214/32/231_2.png) [@Aditya214](https://itensor.discourse.group/u/Aditya214)\
**Post date:** [April 29, 2023, 6:35pm UTC](https://itensor.discourse.group/t/how-to-compute-multisite-exponential-operator-for-dmrg/825/1 "2023-04-29T18:35:50Z")

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Hi, I am using ITENSOR julia version which works well!  
I want to find expectation value of the following operator given by

e^{i \frac{\pi}{2}\sum\_j (1-2n\_j)}

where j ranges from 1 to L (number of sites). and n\_j is fermionic number operators Further I would also like to find expectation value of the operator

n\_1e^{i \frac{\pi}{2}\sum\_j (1-2n\_j)}n\_5

where n\_1 and n\_5 are fermionic number operators at site 1 and 5. I tried lot of methods using Opsum(), however I am unable to compute the value.  
Looking for your kind guidance.