[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).

Konstantin Kudin wrote:
>  Actually, the velocity input appears to be almost purely unsupported.
> Consider these lines in read_cards.f90 :
>           !
>           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

Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu

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