[QE-users] Monitoring the ion velocities in pw.x

[Holzwarth, Natalie]

Dear Paolo,
       Thanks for the information.     The input velocities seem to be OK
when we use the units of bohr/Rytime when Ry=hbar/Ry.   Hopefully this is
correct.    After I sent the email I finally read the  code more carefully
and realized that the velocity is calculated  internally as
vel(t)=(tau(t+dt)-tau(t-dt)/(2dt).    Since the tau values are in the
output, we could then find the velocity values in postprocessing.   Thanks
again.   Natalie

N. A. W. Holzwarth                                       email:
natalie at wfu.edu
Department of Physics                                  web:
http://www.wfu.edu/~natalie
Wake Forest University                                 phone:
1-336-758-5510
Winston-Salem, NC 27109 USA                     office: Rm. 300 Olin
Physical Lab


On Sat, Jun 6, 2020 at 4:31 PM Paolo Giannozzi <p.giannozzi at gmail.com>
wrote:

> Hi Natalie
>
> I am not aware of any way to monitor the velocities during a MD run with
> the PWscf code. It uses plain Verlet (not velocity Verlet) and this is
> likely the reason why velocities are a little bit neglected. Thank you for
> the info about the existence of "ion_velocities='from_input'". I just added
> it to the documentation. Does anybody know about the units for velocities?
> Should be Ry a.u., can anybody confirm?
>
> Paolo
>
> On Thu, May 21, 2020 at 3:29 AM Holzwarth, Natalie <natalie at wfu.edu>
> wrote:
>
>> Dear quantum espresso community,
>>        We would like to monitor the ion velocities during an MD run  of
>> pw.x and cannot find appropriate key words for that in the documentation.
>> Would we need to modify the code in order to output the  velocities at each
>> time step or is there another way?      Similarly,  we think that we
>> figured out how to set initial velocities in the input file  by adding "
>> ion_velocities = 'from_input'", in the &IONS section and adding "
>> ATOMIC_VELOCITIES" followed by a list for each ion. We could not find this
>>  in the documentation, so hopefully it is correct.    It is a very nice
>> feature (just in case you are tracking subroutine popularities).   Thanks
>> kindly for advice on this.     Sincerely,     Natalie
>>
>> N. A. W. Holzwarth                                       email:
>> natalie at wfu.edu
>> Department of Physics                                  web:
>> http://www.wfu.edu/~natalie
>> Wake Forest University                                 phone:
>> 1-336-758-5510
>> Winston-Salem, NC 27109 USA                     office: Rm. 300 Olin
>> Physical Lab
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>
>
>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
>
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