[CP2K:2248] convergence & cutoff madness

[Toon Verstraelen]

Hi,

Apparently the smear option does help a little with the convergence, but 
it is not yet the solution for everything. I've added these lines to the 
SCF section:


      ADDED_MOS 12
      &SMEAR
        METHOD FERMI_DIRAC
        ELECTRONIC_TEMPERATURE 300
      &END SMEAR


I'm not sure if these parameters are decent, but the table looks 
somewhat better for higher cutoffs:


Number of failed SCF	 10
cutoff [Ry]   energy [kjmol]   time [s]   steps   time per step [s]"
    100.0         369302.38      381.62     250        1.53
    110.0           4309.36      470.68     250        1.88
    120.0           4311.87      491.38     250        1.97
    130.0           1159.26      517.84     250        2.07
    140.0            939.17      503.57     250        2.01
    150.0           2550.13      590.24     250        2.36
    160.0            804.26      105.18      39        2.70
    170.0            354.60       72.56      28        2.59
    180.0            412.98      673.03     250        2.69
    190.0            410.19      109.42      39        2.81
    200.0             79.06      146.17      39        3.75
    210.0             79.17      109.10      28        3.90
    220.0             78.54      283.20      66        4.29
    230.0             86.04     1080.76     250        4.32
    240.0             63.43     1099.63     250        4.40
    250.0             33.38      431.16      87        4.96
    260.0             34.90     1060.15     250        4.24
    270.0             22.10      562.68     111        5.07
    280.0             14.48      294.24      52        5.66
    290.0              5.22      202.16      32        6.32
    300.0              4.17      173.59      32        5.42
    310.0              6.07      194.87      32        6.09
    320.0              0.00      200.38      32        6.26
    330.0              2.18      148.32      32        4.63
    340.0              4.32      184.79      32        5.77
    350.0              4.38      327.02      42        7.79
    360.0              4.37      244.75      29        8.44
    370.0              8.01      334.95      39        8.59
    380.0              8.10      226.42      32        7.08
    390.0             13.16      239.73      32        7.49
    400.0             12.49      247.45      32        7.73


In bottom of the table, the computations are faster and all converge. 
Converged energies do still match with the other table. I'm still not 
sure why the energy increases for the higher cutoffs. It is also 
surprising that a cutoff of 250 does not lead to convergence while 
several lower values do...

cheers,

Toon



Toon Verstraelen wrote:
> Dear CP2K users,
> 
> I'm running a few basic tests to get a better understanding of the 
> relation between SCF convergence and the plane wave cutoff. The table 
> below summarizes a series of trivial energy calculations with different 
> cutoffs. The input files are attached.
> 
> The system in the input is MIL-53-Al, a well-known metal-organic 
> framework. To keep things simple, I've used a very minimal basis 
> (SZV-GTH). The largest basis set exponent is 8.3744350009, which 
> corresponds to a cutoff of 330 Rydberg. (if not mistaken). The 
> functional is blyp.
> 
> There are two weird things in this table:
> 
> 1) The lowest energy is not obtained with the highest cutoff. It gets 
> worse above 320.
> 
> 2) For some high cutoff's there is no SCF convergence. For the low 
> range, up to 150, this is normal. I would not expect this for a cutoff 
> of 330.
> 
> Does somebody know what is going on? The input files are rather simple, 
> but maybe I've put in something pernicious? With larger basis sets, 
> there are more cases where the SCF convergence fails. It becomes 
> practically useless, even when a decent initial guess with a smaller 
> basis set is constructed.
> 
> 
> Number of failed SCF	 10
> cutoff [Ry]   energy [kjmol]   time [s]   #iters   time per iter [s]"
>     100.0         370146.36      841.59     250        3.37
>     110.0           4309.36     1023.83     250        4.10
>     120.0           4311.87     1053.45     250        4.21
>     130.0           1159.84     1099.50     250        4.40
>     140.0            939.17     1166.17     250        4.66
>     150.0           2549.48     1206.51     250        4.83
>     160.0            804.26      227.56      42        5.42
>     170.0            354.60      159.26      29        5.49
>     180.0            412.98      177.18      29        6.11
>     190.0            685.96     1455.42     250        5.82
>     200.0             79.06      199.92      32        6.25
>     210.0             79.17      262.35      40        6.56
>     220.0             78.54      201.22      28        7.19
>     230.0             86.04      218.52      28        7.80
>     240.0             63.43      261.85      35        7.48
>     250.0             33.38     2067.27     250        8.27
>     260.0             34.90     2237.25     250        8.95
>     270.0             22.10      225.49      28        8.05
>     280.0             14.48      458.72      52        8.82
>     290.0              5.22      322.73      32       10.09
>     300.0              4.17      251.49      28        8.98
>     310.0              6.07      319.30      32        9.98
>     320.0              0.00      296.63      29       10.23
>     330.0              2.18     2370.99     250        9.48
>     340.0              4.32      351.99      28       12.57
>     350.0              4.38      398.81      32       12.46
>     360.0              4.37      332.36      25       13.29
>     370.0              8.01      496.19      39       12.72
>     380.0              8.10      368.99      29       12.72
>     390.0             13.16      402.97      29       13.90
>     400.0             12.49      410.13      29       14.14
> 
> 
> cheers,
> 
> Toon
> 
> 
>