[Pw_forum] Which Pseudopotential is good for relaxing BaTiO3? Help me please

[Mojtaba Mirseraji]

Dear Paolo and all users

I want to relax the structures of tetragonal and cubic BaTiO3 (barium titanate)
But when I use some pseudopotentials, I can not reach the correct
lattice parameters.
Unfortunately, I calculate a=4.100 to 4.200 for cubic structure of
BaTiO3 but all articles reported that "a" is about 4.006 and my
results are very different !!!!!!!!!!!!!!
Also, for tetragonal structure a=3.800 to 3.900 and c/a=1.250 to 1.265
!!!!!!!!!!!!!!
but this is reported in some articles, a=3.991 and c/a=1.011 !!!!!!!!!!!!!!!

I used some pseudopotentials such as pz (for PSLibrary, both rrkjus
and kjpaw), pw91 (for PSLibrary, both rrkjus and kjpaw), relpw91 (for
PSLibrary, both rrkjus and kjpaw), pw91 (for Vanderbilt, US) and ....
!!!!!!!!!!!!!
All these did not calculate correctly both lattice parameters and
polarizations, unfortunately !!!!!!!!!!!

Which pseudopotential is good for this job? give me some suggestions, please !!!
In general, I am very disappointed to QE and pseudopotentials

Thanks in advance

Mojtaba Mirseraji
Ph.D. Candidate, theoretical condensed matter physics
Arak Univ.
I.R.IRAN