[Pw_forum] some questions about structure optimizing

[Guoying Gao]

Dear everyone,
     When I am doing the structure optimizing, I met with the
following questions:
     First, I do the scf calculation with the experimental crystal
constants and atomic positions (the phase a is high-pressure one), the
output file gives the right symmetry operations and almost the same
pressure as the experiment.
     Then, I do the structure optimizing under the experimental
pressure with calculation = vc-relax, cell_dynamics=damp-pr. After the
convergence is achieved, we do scf with the optimized parameters,
however, the symmetry operations diminished and the output pressure is
much higher than that of the experiment.   We also tried finding the
optimized results which kept symmetry before the convergence is
achieved and reoptimized,  do scf when the convergence is achieved
again, but the results didn't change a lot.
      We lso tried cell_dynamics=damp-w , different pseudopotentials
and the results changed little.
      Anyone who knows the reason for this will be welcomed.
      Thanks in advance!

                         gao