[Pw_forum] vc-relax and dt

[Stefano de Gironcoli]

Masoud Nahali wrote:
> Dear PWscf Users
>
> Is using and setting the variable "dt" in the vc-relax calculation necessary
> or not ? In the forum are many different suggestions.
the value of dt is needed if you perform damped molecular dynamics. it 
is NOT, nor it is necessary to specify the cell mass (wcell) if you 
relax by bfgs . I would use bfgs... which, by the way,  is the default.

>  Also, how can one
> determine which value of
> the variable "max_seconds" is sufficient and safe. when one does not use the
> "max_seconds" the vc-relax calculation may takes huge time without changing
> the cell
> after a specific time. 
max_seconds has nothing to do with vc-relax... it is a variable that can 
be used to instruct the code to stop cleanly after some specified time 
(that should be shorter than the time-limit if the queue you are using) 
so that the calculation can be restarted smoothly.
Please read the corresponding entry in INPUT_PW.html input description.
>  A comprehensive example for vc-relax calculation
> should be very useful.
>   
VCSexample

> Many Thanks
> Masoud
>
>   
stefano
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