Strange Geometries from all-electron DKH calculations of W(OH)6

[M. Brehm]

Dear community,

I am currently performing some all-electron geometry optimizations of 
W(OH)6 with CP2k to investigate the influence of relativistic effects. For 
the Tungsten atom, I use a basis set from Neese, which is specifically 
contracted for the use with DKH, and otherwise equals a TZVPP basis set 
("SARC-DKH").

Without DKH switched on, everything runs fine. CP2k produces an optimized 
geometry which looks quite reasonable.

Starting from this final geometry, I set up a second calculation, and just 
switched DKH3 on. Within the first steps of the optimization, everything 
looks fine: The hydroxyl groups all come a litter closer to the metal atom, 
exactly like expected from relativistic treatment.

But then, one of the oxygen atoms comes closer and closer to the tungsten, 
much closer than it would be reasonable. The gradient is rising all the 
time, therefore these two atoms are attracting themselves even more the 
closer they penetrate.

Now one could say that the BFGS geometry optimizer just performs 
strange/bad steps. But the strange thing is: The total energy is going down 
all of the time... In the end, when the atoms penetrate, the total energy 
is significantly lower than in the beginning, where the geometry was 
reasonable.

Please find attached a zipped version of the calculation directory, 
including input file, log file, basis set and the trajectory of 
optimization (where you can see how the atoms penetrate).

As already noted: Exactly the same input file, but without the &DKH 
section, worked fine.

I appreciate any hints and suggestions concerning my problem.

Best regards,
Martin
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