[Pw_forum] problem in vc-relax convergence

[l.eslami at srbiau.ac.ir]

Hi all,

We are trying to perform vc-relax calculation for a single layer ZnO 
sheet in the presence of an oxygen vacancy in a 4*4 suppercell. We have 
used espresso-5.4.0. with different psudopotentials such as GGA, 
NORMCONS and non relativistic Pseudopotentials: "O.pbe-mt_fhi.upf and 
Zn.pbe-mt_fhi.upf,  as well as GBRV pseudopotentials: 
“o_pbe_v1.2.uspp.F.UPF” and “zn_pbe_v1.uspp.F.UPF”. The calculations do 
not return any error. However, convergences of force and pressure do not 
occur even after long time running of the calculations. In fact, the 
code starts to decrease force and pressure but after a couple of 
relaxation steps they increase. I would be grateful if anyone could 
kindly give me any piece of advice to solve the problem.
many thanks,

Leila Eslami
Department of physics,
Islamic Azad University,
Tehran, Iran