[Pw_forum] pw.x not able to specity initial ion velocities
Nicola Marzari
marzari at MIT.EDU
Wed Aug 23 22:34:07 CEST 2006
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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