[CPMD-list] MD at fixed tempeature

[Ari.P.Seitsonen at iki.fi]

Dear Dr Jkhurdakar,

>   I'm interested in a molecular dynamics simulation
> of a molecule at 300K. I'm somewhat consfused with 
> the choice of appropriate KEWYWORD to achieve this.
>  I want to calculate averages at 300K. So I'm using
> the 
> following input for the CPMD section. 
>  &CPMD
>     MOLECULAR DYNAMICS CP
>     QUENCH BO
>     EMASS
>      800
>     TIMESTEP
>      25
>     TEMPERATURE
>      300
>     TRAJECTORY SAMPLE
>      10
>     MOVIE
>      5
>  &END
> 
>    My question is if the about input is correct or
> should I use  the keyword TEMPCONTROL IONS followed
> by 300 50 on the next line?
>  Any help or comments would be appreciated.

First of all, if your cluster is not very large, the temperature will
fluctuate quite much during the simulation; you can decrease the
fluctuations somewhat by using a Nose thermostat, but this might lead
to somewhat unphysical trajectories as well.

  Secondly, if you specify only "TEMPERATURE" (same as "TEMPERATURE
IONS") this only specifies the initial temperature, if the initial
structure was relaxed to the global minimum you'll end up at around
half of the initial temperature specified due to equilibration between
kinetic and potential energy. So you can use "TEMPCONTROL IONS", but
please notice that the temperature will fluctuate around the average,
and you shouldn't take physical averages of trajectories with the
rescaling switched on, i.e. the "TEMPCONTROL IONS" should only be used
in the beginning to equilibrate the system.

  Hopefully this helps somewhat.

    Greetings,

       apsi

-- 
-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
 Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
 Tel +41 1 635 44 97 / Fax +41 1 635 68 38 / GSM +41 79 719 09 35      
 Anschrift: Physikalisch Chemisches Institut (PCI), Universität Zürich (UniZh)
 Indirizzo: Winterthurerstraße 190, CH-8057 Zürich
 Address:   Schweiz / Svizzera / Suisse / Svizra / Switzerland