cutoff energy convergence problem with a brucite slab

[Eszter Makkos]

Hi,


I would like to optimise a brucite surface model with CP2K (and continue 
further with adsorption studies). I am a new user of CP2K, but I tried to 
follow the tutorials to create an input and run a SCF calculation with it. 
Brucite (Mg(OH)2) has a layered crystal structure with a hexagonal lattice 
cell. I made a two layered slab with 90 atoms in total for start and I used 
the option PERIODIC XYZ for the cell and for the Poisson calculations. 
Although a simple SCF calculation converged pretty easily in 22 steps (with 
a cut_off energy 400 Ry and rel_cutoff 60 Ry) when I try to converge the 
cutoff energies, I run into problems. The Total energy does not converge, 
it is not even close to the 10E-08 energy difference which was suggested in 
the tutorial (http://www.cp2k.org/howto:converging_cutoff):

      
# Cutoff (Ry) | Total Energy (Ha) | NG on grid 1 | NG on grid 2 | NG on 
grid 3 | NG on grid 4 | NG on grid 5
    100.00      -615.4400995077     169106           83084            32296 
           150                 0
    150.00      -613.5889140772     133746           79710            70940 
           240                 0
    200.00      -613.7087067681     106708           75442            97262 
           5224               0
    250.00      -613.7093656033     103150           68644            92846 
          19996              0
    300.00      -613.7092929853     83074             86032           
 83084           32296             150
    350.00      -613.7094737862     75612             77286           
 99292           32296             150
    400.00      -613.7094938770     69804             67896           
 83292           63404             240
    450.00      -613.7095035985     68764             64982           
 79710           70940             240
    500.00      -613.7095069116     58396             57658           
 89650           78692             240
    550.00      -613.7095524421     53260             56148           
 72742          102246            240
    600.00      -613.7095832788     51740             54968           
 75442           97262            5224
    700.00      -613.7094980637     50068             53572           
 68154           92846            19996
    800.00      -613.7095566028     33992             57114           
 78150           83084            32296



I attached the input file to my email, it would be great if someone had a 
few suggestions what could I try to get it converge.


Best wishes,
Eszter



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