WIKI - (WAS Re: [Pw_forum] question on slow rescaling of velocities)

[Stefano Baroni]

Thank you Edoardo.
Your correspondence demonstrates that it is high time to move the  
documentation to the wiki.
Are you (or any of your collaborators, or any of the subscribers to  
this mailing list) willing to help?
Stefano

On Feb 7, 2007, at 1:46 PM, Eduardo Ariel Menendez P wrote:

>
> Thanks Stefano for the clariying this issue. I have a humble  
> suggestion
> for the documentation (INPUT_PW), which is just a feedback from my own
> doubts and time spent thinking and testing.
>
> This is a section of INPUT_PW
>
> delta_t        REAL ( default = 1.D0 )
>                delta_t = 1                 : every 'nraise' step  
> the actual
>                                              temperature is  
> rescaled to tempw
>                delta_t /= 1 && delta_T > 0 : at each step the  
> temperature is
>                                              multiplied by delta_t;  
> this is
>                                              done rescaling all the  
> velocities.
>                delta_t < 0                 : every 'nraise' steps  
> temperature
>                                              is reduced by -delta_T
>                This keyword is NOT used in the case of variable cell
>                calculations.
>
> This is the way that would be instantly clear to my twin brother or my
> clon, with a few more bytes of disk space.
>
> delta_t        REAL ( default = 1.D0 )
>                delta_t = 1                 : every 'nraise' step  
> the instantaneous
>                                              temperature is  
> rescaled to tempw
>                delta_t /= 1 && delta_T > 0 : at each step the  
> instantaneous temperature is
>                                              multiplied by delta_t;  
> this is
>                                              done rescaling all the  
> velocities. See comment
>                                              below.
>                delta_t < 0                 : every 'nraise' steps  
> the instantaneous temperature
>                                              is reduced by - 
> delta_T. See comment below.
>                This keyword is NOT used in the case of variable cell
>                calculations.
>                The instantaneous temperature is calculated at the  
> end of every
>                ionic move and BEFORE rescaling. This is the  
> temperature reported
>                in the main output.
>                For delta_t /= 1, the actual average rate of heating  
> or cooling
>                should be rougly C*delta_t/(nraise*dt) (C=1 for an
>                ideal gas, C=0.5 for a harmonic solid, theorem of  
> energy
>                equipartition between all quadratic degrees of  
> freedom).
>
> Regards
> Eduardo
>>>

...

>>> 1) IS there somthing wrong in this setting?
>>> 2) Is the net temperature rescaling equal to delta_t*nstep/ 
>>> nraise, or this
>>> is only an estimate?
>>> 3) It seems that I must either scale longer time or increase  
>>> delta_t. Is
>>> there any other option?
>>>
>>> Thanks
>>> Eduardo
>>> _______________________________________________
> k
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum

---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

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