[CP2K-user] [CP2K:18518] Accuracy required for BOMD?

[Rodolphe Pollet]

Dear CP2K users and developpers,

I plan to study a reaction between two organic molecules in aqueous 
solution.

First I did some preliminary (RUN_TYPE ENERGY) tests for this fixed set of 
parameters
      
      NGRIDS 4
      REL_CUTOFF 60

      EPS_DEFAULT 1.0E-12

      EPS_SCF 5.e-7

for the following cutoffs: 100, 200, 300, 400, 500, 600, 700, 800, 900, 
1000, 1100, 1200.

The plot of the energy (see first attachment) and the accuracy of the 
density at 400 Ry

  Electronic density on regular grids:      -1041.9999999944       
 0.0000000056
  Core density on regular grids:             1041.9999999996       
-0.0000000004

show that 400 Ry seems OK although the rule that states that the largest 
exponent (here 10.389228018317, for oxygen) times REL_CUTOFF (60 Ry) should 
be less than CUTOFF is not satisfied.

Then I did a BOMD at this cutoff but changing these two different parameters

     EPS_DEFAULT 1.0E-10

    EPS_SCF 1.e-6

so that the accuracy on density has decreased (now more than 1e-8)

  Electronic density on regular grids:      -1041.9999999900       
 0.0000000100
  Core density on regular grids:             1041.9999999628       
-0.0000000372

However the conserved quantity during the MD seems OK (see second plot).

In your opinion, is the accuracy of this trajectory high enough or did I 
choose wrong parameters?

Thanks in advance

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