[CP2K-user] [CP2K:17135] Re: "Fastest" AIMD simulation settings/parameters

[Nicholas Winner]

Here's a list of some things I can think of to increase speed. Probably not 
comprehensive. In the future include your input file for people so we can 
see what settings you are already trying.

Will not compromise accuracy (test all options to find best)

   1. Using traditional diagonalization:
      1. Use broyden mixer, which is generally (not always!) faster. 
      2. In broyden use as large of a alpha value as you can afford while 
      still achieving convergence.
   2. Using OT:
      1. Change preconditioner to speed up the scf convergence. Normally 
      Full_all or Full_single_inverse are most effective, but full_kinetic might 
      be good if you have a huge system that takes too long to precondition.
      2. if you know the system energy gap, you can supply a slight 
      underestimate of it to the OT preconditioner to help it converge faster
      3. Change from CG (which is more robust) to DIIS which is usually 
      faster
   3. Use ASPC wfn extrapolation
   4. Inspect your SCF convergence. If you see unstable long convergence, 
   then increasing your precision settings might help you in the long run.

Will/might compromise accuracy

   1. Decrease EPS_DEFAULT 
   2. Decrease EPS_SCF (tolerance for scf convergence)
   3. Use UKS = False. I.e. spin unpolarized if you not need it.
   4. Use a larger MD time-step. Some systems are still okay with a large 
   time step of 2fs, could work for you.

-Nick
On Sunday, June 12, 2022 at 12:06:49 PM UTC-7 lenardc... at gmail.com wrote:

> Just replying to this to bump it higher since I haven't received a 
> response yet.
>
> On Thursday, June 9, 2022 at 3:38:02 AM UTC+2 ASSIDUO Network wrote:
>
>> Hi there, I have been running AIMD simulations for about a year now and 
>> it originally started off really slow, only getting 60 fs per day. In 
>> particular, I used the NVT ensemble and the Nose-Hoover thermostat. When 
>> swapping to the Langevin ensemble and adaptive-Langevin thermostat, the 
>> simulation time improved to 200-600 fs a day. 
>>
>> I wanted to know what settings/parameters you would suggest to improve 
>> the speed even further? That is, what are the best settings to choose to 
>> get the fastest performance?
>>
>> Key things to keep in mind for my work:
>> Using GTH-PBE potential and the DZVP-MOLOPT-SR-GTH basis set. Fermi dirac 
>> smearing must also be used 
>>
>

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