[QE-users] Essential of doing vc-relax - regarding

[singaravelan T R]

Dear all,
I like to know the difference between vc-relax (*optimize lattice constant
and atomic positions)  *and relax(*optimize the atomic positions alone*).
other than the bold words, i like to know further.? and also  When to
perform vc-relax?
Is vc-relax superior over relax part. ?
I have two views which are correct, I don't know, following are those:
please help me here.
1) Suppose if i am doing vc relax for silicon and i got some cell
parameters and atomic position. Is that the atomic position and lattice
constant I should use for further scf calculation? (I am saying No need to
do lattice constant optimization.)
 *(or)*
2) I haven't done vc-relax, just done a relax calculation with reference
lattice constant, i used that atomic position in my further calculation,
proceeded with ecutwfc optimization, then kpoint, lattice constant ? (Not
worried on vc relax).
Which is correct?
with thanks,
Singaravelan T R
Research Scholar,
University of Madras
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