K-Points and Extrapolation

M. Brehm brehmin... at gmail.com
Sat Sep 15 12:13:57 CEST 2018


Hi Juerg,

I noticed that you recently implemented several extrapolation methods for 
use with K points. I was curious and set up a small example calculation. I 
adapted the regtest "QS/regtest-kp-1/c_2.inp": I increased the cutoff to a 
reasonable value, switched to Broyden Mixing, moved one of the carbon atoms 
a little off its lattice position, and made a geometry optimization (with 4 
steps) out of it.

Please find attached my test input file as "c_2.inp". For my tests, I used 
the current CP2k trunk version.

I tried the four allowed values LINEAR_P, USE_GUESS, USE_PREV_P, and 
USE_PREV_RHO_R as choices for EXTRAPOLATION. Please see attached the four 
log files which resulted from these four runs.

It seems that all three "true" extrapolation methods do not work as 
expected. The quality of the extrapolated initial wave function is a lot 
poorer than the initial guess, with "convergence" values in the order of 20 
- 200.

I would be grateful if somebody would have a look what goes wrong in this 
example.

Thanks and with best regards,
Martin

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