[Pw_forum] Specifying initial velocities in MD

[Ilya Ryabinkin]

Well, I figured it out by myself... Here is a short tutorial for those
who might be interested.

All below is pertinent to QE 5.2.1.
There is an undocumented feature allowing one to specify initial velocities.

1. Add  to the input list
&IONS
ion_velocities = 'from_input'
/

2. Add a new input card "ATOMIC_VELOCITIES".

Here is the quotation from the source code (read_card_f90):
   ! ATOMIC_VELOCITIES
   !
   !   read velocities (in atomic units) from standard input
   !
   ! Syntax:
   !
   !   ATOMIC_VELOCITIES
   !     label(1)  Vx(1) Vy(1) Vz(1)
   !     ....
   !     label(n)  Vx(n) Vy(n) Vz(n)
   !
   ! Example:
   !
   !   ???
   !
   ! Where:
   !
   !   label (character(len=4))       atomic label
   !   Vx(:), Vy(:) and Vz(:) (REAL)  x, y and z velocity components of
   !                                  the ions
   !


Two caveats:
Caveat #1. Velocities are given in bohr/1Rut, not in atomic units as
the source says!

Caveat #2. If there are no frozen atoms in a cell, the center-of-mass
velocity will be subtracted from
the given velocities leading to a different value of the initial
kinetic energy. If any of atomic coordinate is
frozen, the velocities are assigned as given.


-- 
*******************************************************
                    Ilya Ryabinkin
                 Postdoctoral Scholar
          Physical and Environmental Sciences
           University of Toronto Scarborough
  http://www.utsc.utoronto.ca/~aizmaylov/Members.html
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