[Wien] Lattice parameters in the SCF cycle

[Indika udaya]

Dear WiEn2k experts
I recently started WIEn2k. I have a basic question on optimization of the structure which I am confused on. 

I need to get the lattice parameters with and without adding Hubbard U and spin orbital coupling to my structure. For that I started with the experimental values and performed the SCF cycle. It converged with cc 0.0001 and ec 0.00001. But I noticed the initial lattice parameters I started remains the same until the last iteration of the scf cycle ( at the 53rd iteration).
Then I added hubbard U (5eV) to the calculation and finished the scf with same convergence criteria. Next finished scf with U+SO. 
But in all the cycles lattice parameter did not change.
I am not sure whether this observation is correct with WIEN2k *( or i am missing something during the calculation??)
If so, how do I check the changes of lattice parameters with Hubbard-U and SO?? Do I need to do volume optimization for each of the steps (namely for scf, SCF+U and for SCF+U+SO seperately) and use the lattice parameters at minimum energy position ?
Thank you for your time and I am waiting for a quick responce.
IndikaPhD Candidate

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