No cutoff converge for water slab system

[Ivan Gladich]

Dear CP2K community,


I would like to simulate a small organic molecule, MethylGlyoxal, on a 
liquid water interface comprising of 216 water molecules.

The total number of atoms in my simulation box is 657 atoms and 20 A X 20 A 
X 60 A size, with two liquid-water/vacuum interfaces along the z-direction.

This system has been previously equilibrated by classical MD.


I am writing you because I am not able to reach a reasonable convergence 
for the cutoff. On the other hand, the rel_cutoff the behavior looks 
reasonable. 

I am a bit puzzled because, looking at the literature, several works using 
liquid water slab were performed with cutoff of 280 Ry (or similar).

Here, even with 400 Ry I cannot see a reasonable convergence. 

I tried to look in the mailing list, exploring different options but 
without success.


You can find attached my input files.

Moreover, how the performance of my runs would be affected using a large 
cutoff?


Thank you very much for any possible help or hint.. I am a newbie in cp2k. 


Ivan



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::::::::::::::

# Grid cutoff vs total energy

# Date: Tue Oct  4 15:14:43 AST 2016

# REL_CUTOFF = 60

# Cutoff (Ry) | Total Energy (Ha) | NG on grid 1 | NG on grid 2 | NG on 
grid 3 | NG on grid 4

    150.00  -3601.3810732568  6355937  1954418  1677530  1532857

    200.00  -3602.4707815085  5617861  2264331  1690695  1947855

    250.00  -3603.0017495985  5385050  1981561  2003927  2150204

    300.00  -3603.5954834995  4713771  2383273  1993480  2430218

    350.00  -3603.8647277931  4575375  2443492  1787867  2714008

    400.00  -3604.2212237954  4160605  2491335  2066041  2802761

    450.00  -3604.4406345606  4014931  2341006  1954418  3210387

    500.00  -3604.6475134416  3777337  2142718  2204241  3396446

    550.00  -3604.8761360971  3647230  2133733  2123763  3616016

    600.00  -3605.0089346664  3581670  2036191  2264331  3638550

    650.00  -3605.2009691021  3505781  1965487  2039270  4010204

    700.00  -3605.2009689802  2988139  2429724  1948748  4154131

    750.00  -3605.4377935718  2895507  2489543  1981561  4154131

::::::::::::::

rel_cutoff_data.ssv

::::::::::::::

# Rel Grid cutoff vs total energy

# Date: Tue Oct  4 15:14:44 AST 2016

# CUTOFF = 400

# Rel Cutoff (Ry) | Total Energy (Ha) | NG on grid 1 | NG on grid 2 | NG on 
grid 3 | NG on grid 4

     10.00  -3609.6346138640  315656  2541164  2201475  6462447

     20.00  -3604.4859689279  1815123  2345482  2491335  4868802

     30.00  -3604.2265167341  2856820  2201475  2302172  4160275

     40.00  -3604.2214496779  3581670  2036191  2264331  3638550

     50.00  -3604.2212362541  3921274  2123947  2079075  3396446

     60.00  -3604.2212237954  4160605  2491335  2066041  2802761

     70.00  -3604.2212216269  4595916  2422951  1787867  2714008

     80.00  -3604.2212216266  4713771  2383273  1993480  2430218

     90.00  -3604.2212216259  5058295  2302172  2010071  2150204

    100.00  -3604.2212216259  5385050  1981561  2020317  2133814


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