[Pw_forum] Run using a relaxed structure as initial one NOT converge in fir st few ionic steps.

[Giovanni Cantele]

> On 20 Dec 2016, at 10:26, quantum <quantum at mail.ncyu.edu.tw> wrote:
> 
> 
> Dear QE Friends:
> 
> I did a "relax" calculation with PW (version 5.3.0)
> and obtained the relaxed atomic positions.
> 
> Then, I took the atomic positions
> in the last "ATOMIC_POSITIONS (crystal)"
> section of the output file to replace the
> atomic positions in the original input file
> without changing any other things except new
> prefix and outdir.
> 
> The atoms in the relaxed structure should
> all satisfy etot_conv_thr and forc_conv_thr
> thresholds.  With this in mind, I started
> the new run.
> 
> I expected the run to
> converge after the first or two ionic steps.
> But it did not stop, and continued running
> for many ionic steps without convergence.
> 
> Is my expectation correct? or it is a problem
> of QE?
> 
> Sincerely,
> Tsung-Lung Li
> 
> 
> Tsung-Lung Li, Ph. D.
> Professor
> Department of Applied Physics
> National Chia-Yi University
> 300 Hsueh-Fu Road, Chiayi 60004, Taiwan
> Phone: 886-5-2717904.  FAX: 886-5-2717909.
> E-mail:quantum at mail.ncyu.edu.tw    
> URL:http://web.ncyu.edu.tw/~quantum
> 
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> 

Generally speaking, unless very odd behaviour is taking place, your expectation is correct but it is NOT a problem of QE.
If you paste relaxed positions into the SAME input file QE converges with NO further ionic steps. Maybe try to provide the two input files (the one with unrelaxed positions and the one with related positions) as well as the outputs to understand what is going on.

Giovanni