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

[stewart at cnf.cornell.edu]

Hi Stefano, 

The front page for the QE wiki is edit protected.  I think it would be 
useful to add a link from there to Documentation.  Once someone puts that in 
place, I would be glad to put up some of the INPUT_* files on the 
Documentation wiki page. 

Regards, 

Derek 


Stefano Baroni writes: 

> 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
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>> Pw_forum at pwscf.org
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> 
> ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
> Trieste
> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) 
> 
> Please, if possible, don't  send me MS Word or PowerPoint attachments
> Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html 
> 
>  
> 
 


################################
Derek Stewart, Ph. D.
Scientific Computation Associate
250 Duffield Hall
Cornell Nanoscale Facility (CNF)
Ithaca, NY 14853
stewart (at) cnf.cornell.edu
(607) 255-2856