[DFTB-Plus-User] OpenMP scaling questions

[Yang, Chi-Ta]

Greetings,


I am using dftbplus-18.2, and testing the "core" and "calculation time" upon a system as below.


Test system details:

- 809 atoms and periodic
- Gamma point k-point sampling

I was running on jobs with 20, 30, and 40 cores, but the elapsed time are comparable.
20 cores job:  13:36:16 hours
30 cores job:  15:14:54 hours
40 cores job:  12:12:32 hour

The outputs show the OpenMP threads were as expected, but the 40-cores job didn't get the benefit as compared to 20-cores job.

Could you please help why there is no scaling?


BTW,  the running time shows ***** as below. Is there a way to show the full digits.
--------------------------------------------------------------------------------
DFTB+ running times                          cpu [s]             wall clock [s]
--------------------------------------------------------------------------------
Sparse H0 and S build              16557.11  (  1.6%)    423.90  ( -0.2%)
SCC                                    + ********  ( 87.8%)  ********  (104.3%)
Diagonalisation                        ********  ( 63.4%)  ********  (108.9%)


Thanks a lot,
Chi-Ta Yang







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