Reading/Specifying forcefields with FIST

[Nuri Yazdani]

Hi All,

I dont any experience with MM, but I am quite interested in the QM/MM 
capabilities of CP2K, so I am starting to dabble. I'm trying to first run 
some MM calculations, unfortunately, having a large number of problems!! 
The problem that mainly concerns me is with the reading/ specifying the 
interactions.

I ran a calculation on a single ligand, using some files I got from the 
SWISSPARAM, these are the meeaa.* files attached. The geometry optimization 
seems to work well and give reasonable results for the molecular structure. 
Next I wanted to run a system with a small crystallite, with only 
non-bonded interactions, the idea being afterwards to run a mixed 
simulation with the crystalite and the ligand from above. 

First I ran the calculation (cdse_manual.*) specifying all of the 
Non-bonded interactions in the cp2k input file. This also seemed to work 
well and give sensible results.

Now, I tried to redo this calculation, but now added the non-bonded 
interactions  for the crystallite to the .par file which contains the 
interactions for the ligand, and read the FF from that file (cdse.* files). 
The resulting geometry optimization gives an exploding crystallite, and it 
is clear the non-bonded interactions are not the same as in the cdse_manual 
calculations. What am I doing wrong here?? Most concerning for me, is that 
now I dont completely trust that the non-bonded interactions for the ligand 
(meeaa run from above) are being used properly from the par file!

I also checked that if I remove the non-bonded interactions from the .par 
file, that the calculation gives me an error flag that the non-bonded 
interactions are not specified, so they are being read, just not used the 
same as when I specify them manually in the input file.

If anyone can shed some light on this for me I would be very grateful!
Cheers,
Nuri
 
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