graphite in CP2K

[Michele Ceriotti]

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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