graphite in CP2K

[Matthias Krack]

Hi Michele,

I would suggest to set EPS_DEFAULT in @QS section at least to 1.0E-12 or 
lower and for the ALPHA in &MIXING I would also use a smaller value like 
0.2. Maybe this will help to converge your system properly.

Matthias

On Wednesday, May 28, 2014 4:20:44 PM UTC+2, Michele Ceriotti wrote:
>
> Dear CP2K community, 
>
>      I have been trying for a few days to set up calculations of graphite 
> as an exercise for a student but I am getting the weirdest results.  I am 
> sure in the it will end up being a silly mistake in the input, but I can't 
> get to see it so perhaps someone can help. 
>
> Despite using a fairly large FD smearing, the SCF cycle has a hard time 
> converging, and when the maximum number of steps is reached 
>
>     50 Broy./Diag. 0.50E+00    1.2     0.00014351      -819.2909959720 
> -2.28E-09
>   *** SCF run NOT converged ***
>
> and the calculation carries on with what it has got, diagnostics are 
> really strange. 
>
> For a start, eigenvalues show two weird very low-energy states
>  MO EIGENVALUES AND MO OCCUPATION NUMBERS
> # MO index          MO eigenvalue [a.u.]            MO occupation
>          1                    -21.523076                 2.000000
>          2                    -21.517160                 2.000000
>          3                     -1.383548                 2.000000
>          4                     -0.510418                 2.000000
>
> forces on the atoms are insane
>  ATOMIC FORCES in [a.u.]
>  # Atom   Kind   Element          X              Y              Z
>       1      1      C           4.68736611     4.63921800  -222.86999309
>       2      1      C          -1.57720920    -4.48651652   124.33822840
>       3      1      C          -5.01734639     3.10518104   176.16292919
>
> and so is the stress tensor
>  STRESS TENSOR [GPa]
>             X               Y               Z
>   X   -8233.84728056      8.05482610      0.90481573
>   Y       8.05482610  -9552.76932222     -0.49445437
>   Z       0.90481573     -0.49445437  -2526.59040628
>
> I was thinking of an error in the structure or the cell parameters, but I 
> checked it many times and everything seems in order. The same structure, 
> with same functional and similar parameters in SIESTA converges like a 
> stone, and gives no problem whatsoever. 
>  
> Can you spot something obvious that I am missing? I'd really like to use 
> CP2K for this exercise, but I can't seem to figure out what is going wrong. 
>
> Many thanks,
> Michele
>
>
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