[Pw_forum] MD restart algorithm in Quantum Espresso

[Alexey Akimov]

Dear all,

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