[CP2K-user] Kpoints, Diagonalization algorithm and Mixing

Marcella Iannuzzi marci... at gmail.com
Wed Sep 23 08:40:50 UTC 2020

Dear Lucas, 

With OT you can try other preconditioners.
The best would be FULL_ALL, but is also the slowest. FULL_SINGLE_INVERSE 
should be a good compromise. 
With the diagonalisation the extrapolation is probably better using the 
previous wavefunction. 
To speed up MD you can also consider to make the convergence criteria less 
tight, but keep an eye on the conservation of the total energy.

Kind regards

On Wednesday, September 23, 2020 at 7:40:34 AM UTC+2 Lucas Lodeiro wrote:

> Hello all,
> I am trying to improve the performance of MD steps for a big slab system 
> which contains Cu atoms... the systems has ~1500 electrons and needs 2x2x1 
> kpoints to compute their electronic structure (as we explore in a PW based 
> program, Quantum Espresso). 
> The first approach was to use multiple_cell 2 2 1 with just a Gamma point 
> and &OT method (with FULL_KINETIC preconditioner). The system is well 
> behaved and works fine, but the time needed for each frame is a little high 
> (87s per frame) to compute long MD.
> As a second approach, to explore if there are a method to speed up the MD, 
> we use multiple_cell 1 1 1 and 2x2x1 kpoints, with standart diagonalization 
> algorithm with broyden mixing (attached file), but the performance is not 
> so good, mainly in the extrapolation step, where ASPC cannot be used. We 
> explore LINEAR_P, and previous P and Rho, but this does not work fine... 
> and needs several SCF steps to converge.
> The combinations for Diagonalization algorithm and mixing are various and 
> I prefer to ask if there is a way to improve diagonalization based 
> calculations.
> As the system is well behaved, is it an advantage to use another algorithm 
> and mixing method?
> Could be a diagonalization-kpoint calculation faster than the analogous 
> one with OT? 
> Another thing is based on the kpoint scheme... We want to use a 2x2x1 
> gamma centered grid... but I am not clear about MONKHORST-PACK is the Gamma 
> centered or displaced grid. MACDONALD and GENERAL, which are their 
> differences? I am familiar with the Quantum-Espresso kpoint scheme.
> There are a lot of questions, sorry, but I need some insight to not search 
> in the fog, one by one.
> Regards - Lucas Lodeiro
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