[Pw_forum] about 'md'

[Nicola Marzari]

As a side note, if you have the positions along a trajectories,
you can reverse engineer the velocities:

v(t)=(x(t+delta)-x(t-delta))/(2*delta)

(easy to see: do a series expansion of x(t), around t, in powers of
the timestep delta).

			nicola


Paolo Giannozzi wrote:
> On Tuesday 25 December 2007 17:07, Dongdong Kang wrote:
> 
>>   I want to use 'md' (in pwscf) to calculate vibrational property about
>> some materials. but when i check the output file, there aren't ion
>> velocities in it.   How can i get ion velocities in 'md' ?
> 
> you have to modify PW/dynamics-module.f90 so that saves somewhere 
> the velocities (they should be in array "vel"). PWscf uses the plain verlet
> algorithm, not the velocity verlet. Until  now nobody has felt the need to
> know about velocities, so they were not saved
> 
> Paolo


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Prof Nicola Marzari   Department of Materials Science and Engineering
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