[CP2K-user] [CP2K:19324] ETRS and CN propagators lead to completely different Ehrenfest dynamics

[Natalia K]

Dear CP2K team,

I performed simple tests for H2 with cp2k-9.1 using an input file from 
*cp2k/tests/QS/regtest-rtp-2* and modifying the external field (the input 
file is attached). I then performed 4 tests, using ETRS or CN propagators 
and two different time steps, dt=0.25 a.u. and 0.125 a.u. With the ETRS 
propagator, the energies as well as the H atom dynamics are the same for 
both dt values. However, the results with the Crank-Nicolson propagator 
(CN) are not only different for two time steps, but also are completely 
different from when using ETRS. I attach the results here. I tried refining 
some other parameters, but the two propagators always lead to different EMD.

My question: when performing Ehrenfest dynamics with applied external 
field, which propagator should I trust? Why they give such different 
results?

Best regards,

Natalia

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