[Pw_forum] MD restart algorithm in Quantum Espresso

[Paolo Giannozzi]

About the first point: are you referring to MD on the ground state
("Born-Oppenheimer" MD), done with PWscf (not Car-Parrinello)?
I think that the restart does the correct thing, i.e. use the Verlet
algorithm as if the run was not interrupted, but there might be
some subtle differences in how the threshold for convergence is
calculated, that are more than sufficient to have the two MD
simulations diverge.

About the difference between nstep and the number of steps actually
performed: it shouldn't be difficult to follow variable "nstep" and  
see why
this happen

P.
On Aug 1, 2012, at 24:51 , Alexey Akimov wrote:

> I tried to perform md simulations in Quantum Espresso in 2  
> different ways:
> 1) simply run a single continuous trajectory (e.g. 10 steps)
> 2) run first step of MD as a new calculation (restart_mode =  
> from_scratch, default)
>   and run all other (remaining 9) steps as restarts (restart_mode =  
> restart), doing this for every step
>
> As a result after a few steps the total energies, atomic forces and  
> position started to deviate between two approaches.
>
> I suspect that some information from the previous step may be  
> dropped during the restart (e.g. by using the first-order Euler  
> scheme instead of the Verlet algorithm), eventually leading to such  
> divergence. So my question is: what is restart algorithm for MD in  
> quantum espresso and is there any possibility to use method 2 (see  
> above) without accumulation of the integration errors?
>
> Also can someone clarify why if i specify nstep = 1 in my input  
> file (request to perform a single MD step), the program actually  
> makes 2 MD steps?
>
>
> Thank you,
> Alexey
>
>
>
>
> -- 
> Dr. Alexey V. Akimov
>
> Postdoctoral Research Associate
> Department of Chemistry
> University of Rochester
>
> aakimov at z.rochester.edu
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---
Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222