[QE-users] Is it necessary to do "vc-relax" with pw.x before doing CPMD with cp.x ?

[likejiang at ustb.edu.cn]

Dear QE-Users,

I am doing CPMD with cp.x for iron oxide system following the official
tutorial which introduced two steps (Step1: Reaching the electronic ground
state; Step 2: Relax the system) before doing cpmd.

However, in both the electronic minimization and ionic minimization
processes, I found that the force cannot converge (forc_conv_thr=1.0D-3
cannot be satisfied), while it is relative easy for electronic energy and
total energy to converge (ekin_conv_thr=1.0D-6, etot_conv_thr= 1.0D-4). 

I am wondering whether this is caused by that the initial crystal structure
is not fully relaxed with the current pseudopotential. Is it necessary to do
"vc-relax" with pw.x before doing CPMD with cp.x ?  If yes, which parameters
should be kept to be the same in both pw.x and cp.x?

Any comment or suggestion will be much appreciated.

Thanks,
Kejiang

-------------------------------------------------
Dr. Kejiang Li
School of Metallurgical and Ecological Engineering,
University of Science and Technology Beijing
Xueyuan Rd., Haidian District, Beijing 100083, P. R. China
https://kejiangli.com/

 

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