[Pw_forum] pw.x not able to specity initial ion velocities

[Nicola Marzari]

A side comment: initializing velocities makes sense for a
born-oppenheimer simulation, but not for a car-parrinello one.

In the latter case, the electronic wavefunctions must acquire a
dynamics that follows quasi-adiabatically the ionic one. So, one wants
to avoid an abrupt start (i.e. ionic velocities different from zero)
since this would excite a number of frequencies in the
electronic evolution (that we do not want, would lower the quality of
the simulation, and that would take a lot of time to thermalize out).
	
			nicola


Konstantin Kudin wrote:
>  Actually, the velocity input appears to be almost purely unsupported.
> Consider these lines in read_cards.f90 :
> 
>        ELSE IF ( TRIM(card) == 'ATOMIC_VELOCITIES' ) THEN
>           !
>           CALL card_ion_velocities( input_line )
>           IF ( ( prog == 'PW' .OR. prog == 'CP' ) .AND. ionode ) &
>              WRITE( stdout,'(A)') 'Warning: card '//trim(input_line)//'
> ignored'
> 
>  What this piece of code is saying is that for either PW or CP the
> ATOMIC_VELOCITIES card is ignored (when is it supported then?). While
> this of course does not guarantee that this message is reliable, my own
> experience with trying to input velocities into CP seems to confirm the
> lack of such functionality.
> 
>  Kostya


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