[Pw_forum] vc-relax

[alan chen]

Dear PWSCF users,
    I try to relax the z-axis of STO while its x- and y-axis are fixed (i.e.
relax STO under strain). I use 'vc-relax' and cell_dofree=z. The
ion-dynamics is 'damp' and cell_dynamics is 'damp-w'. However I found that
this 'Wentzcovitch Damped Dynamics' always does 50 iterations and stops. But
the strain along the z direction is not necessarily the smallest after 50
iterations. Usually the z-strain is smallest after some iterations (for
example 30 iterations) then it goes up.
   I want to ask why the code does not pick up the value of lattice
constant of z direction which minimizes the strain in the z direction but
just picks up the final value of  lattice constant after 50 iterations?
   Thank you very much.

Hanghui Chen
Department of Physics
Yale University
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