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<p>Hi<br>
</p>
<p>0) the merge request was accepted, so just download the develop
branch from <a class="moz-txt-link-freetext"
href="https://gitlab.com/QEF/q-e">https://gitlab.com/QEF/q-e</a></p>
<p>1) larger with respect to the system at equilibrium evolved with
wft starting with zero velocity? If you give velocities to
electrons they will have kinetic energy, that has to be greater,
for example, to the kinetic energy of the electrons after a
minimization.<br>
</p>
<p>2) Don't know, there are so many variables... what is the system?
how many steps? is it expensive? what are the typical correlation
times of the system? ... Knowing nothing, my general suggestion to
perform equilibration is to do an initial cheap
easy-to-equilibrate classical molecular dynamics simulation with
your favorite force field (not necessarily a sophisticated one)
and your favorite code. Then use a snapshot of the equilibrated
classical molecular simulation as a starting point for the
car-parrinello one (be careful to the units of velocities: same
units specified for the input of the positions divided by time in
atomic units). Getting equilibrium in cp should be easier with
this initial condition.<br>
</p>
<p>3) ion_velocities = 'from_input' works also with
restart_mode='restart', the documentation will be corrected soon.
But usually ionic and wfc velocities are read from the restart
file, not from input, after you started the simulation (unless you
want to manually change the velocity of some atoms). Wfc is always
saved in the restart, why you said that it would be random?</p>
<p><br>
</p>
<p>best,<br>
</p>
<p>Riccardo Bertossa</p>
<div class="moz-cite-prefix">Il 23/10/18 19:34, Eduardo Menendez ha
scritto:<br>
</div>
<blockquote type="cite"
cite="mid:CAM5Vcw-J1H-N833qujBao3By7KqOSo+61VWLwsw1RcwN05LmMQ@mail.gmail.com">
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<div>Thank you Riccardo. I followed the link you pointed and I
see the issue is fixed, but I do not know how to download
the fixed source file(s).<br>
</div>
<div><br>
</div>
<div>I have more doubts. <br>
</div>
<div><br>
</div>
<div>1) I have twice tested the procedure of doing 2 CG steps,
then restart the CP simulation. In both cases I have gotten
an increased electron kinetic energy, significantly larger
than before the CG steps. <br>
</div>
<div><br>
</div>
<div>2) I have succeded to give initial velocities via random
initial positions, followed by velocity rescaling, but I
stil do not get equilibrium. I find an intriguing statement
about the mean square displacements <br>
</div>
<div><br>
</div>
<div> Partial temperatures (for each ionic specie) <br>
Species Temp (K) Mean Square Displacement (a.u.)<br>
1 5.54E+02 1.9353E+03<br>
2 3.12E+02 1.9354E+03<br>
3 2.52E+01 1.9352E+03<br>
4 5.43E+02 1.9354E+03<br>
5 1.03E+02 1.9355E+03</div>
<div><br>
</div>
<div>3) finally, regarding the documentation statement: <br>
</div>
<div>
<pre><pre>'ATOMIC_VELOCITIES'
BEWARE: works only if restart_mode='from_scratch',
tested only with electrons_dynamics='cg'</pre></pre>
</div>
<div>I guess one cannot use 'sd' or 'cp', unless it admits
restart_mode='restart', otherwise the wfc would be random.
Am I missing something?<br>
</div>
<div><br>
</div>
<div>Best regards, <br>
</div>
<div><br>
</div>
<div>
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<div>Eduardo Menendez Proupin</div>
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<div><br>
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<div>---------- Forwarded message
----------<br>
From: Riccardo Bertossa <<a
href="mailto:rbertoss@sissa.it"
target="_blank"
moz-do-not-send="true">rbertoss@sissa.it</a>><br>
To: <a
href="mailto:users@lists.quantum-espresso.org"
target="_blank"
moz-do-not-send="true">users@lists.quantum-espresso.org</a><br>
Cc: <br>
Bcc: <br>
Date: Tue, 23 Oct 2018 10:53:28
+0200<br>
Subject: Re: [QE-users] how to
obtain random initial velocities
with CP<br>
<div bgcolor="#FFFFFF">
<pre>Hi,
I had too the issue with starting random velocities.
I think I've fixed it in the merge request <a class="gmail-m_-3424302602125242313moz-txt-link-freetext" href="https://gitlab.com/QEF/q-e/merge_requests/189" target="_blank" moz-do-not-send="true">https://gitlab.com/QEF/q-e/merge_requests/189</a>, can you please give it a try?
Regarding the reading of the velocities from the input:
the documentation was wrong, because the units of the velocities were not correctly stated, it was corrected few months ago. I think that it works also without CG.
But please note that after manually setting the velocities you should do a step of CG, that in fact does two steps in this case
(one with the starting ions position and one with the position updated with the new velocities), to set the initial wavefunction velocity to a reasonable value with respect to the ions velocities.
In my experience, if you don't do this, the kinetic energy that the wfc gain at the end is bigger than the kinetic energy that you get with the electron velocities calculated in the "correct" way.
Note also that in the new version, I added an option "change_step" also for the electron_velocities when you change step. This was a little modification to allow a smoother change
(before the electron velocities was not updated if the timestep changed, increasing the kinetic energy of the electrons that were no more moving, in some sense, following the ions).
</pre>
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<blockquote>
<pre>'zero' : restart setting electronic velocities to zero
'default' : restart using electronic velocities of the
previous run
'change_step' : restart simulation using electronic velocities of the
previous run, with rescaling due to the timestep change.
specify the old step via tolp as in
tolp = 'old_time_step_value' in au.
Note that you may want to specify
ion_velocities = 'change_step'
</pre>
</blockquote>
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<pre>Note also that the change of dt is correctly implemented in the autopilot module
(so, it is not necessary to use a restart file, and you can change easily dt on the fly and try more values of it)
Best regards
Riccardo Bertossa</pre>
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