[CP2K-user] [CP2K:21404] RESP charges for simple molecule is poor

[Andreas Döll]

Hello,

I want to do a RESP fit to determine the partial charges for a simple 
molecule in cp2k. My molecule has 18 atoms. I already looked in past 
discussions on RESP charges and my questions are not resolved. My procedure 
was:

-Optimize the geometry in cp2k
-Do a single point calculation with the optimized geometry 
-Fit the RESP charges to obtain the partial charges

I do have the partial charges of this molecule from a paper and from a DFT 
calculation using gamess (with different XC/BASIS) so I can compare the 
cp2k results to the "ground truth". 
In my opinion the charges obtained via cp2k are quite off. I fixed lots of 
charges by using the REPEAT method in a periodic box, but my carbons are 
off!
I am unsure if this is due to some settings I use, like an inappropriate 
Basisset/potential when doing my SCF calculation or if my RESP fit is poor, 
although my RMS seems good.

WHAT I TRIED:
-If I restrict my charges close to the target charges I get more reasonable 
results, but obviously this approach is nonsense when doing an unknown 
system (which will be a COF structure in the future). So far I have been 
using a strength of 0.001.  I also tried using constraints to impose equal 
charges, but still the charges on my molecule deviate from my expected 
results (this symmetry based assumption I can use in the future for the COF 
system).

-I tried different basis set and XC but it didnt seem to improve much. 

-I used the optimized geometry from gamess and cp2k as input and both 
result in unrealistic charges

-I used REPEAT METHOD in a periodic box, even though my testsystem was 
originally in a nonperiodic box and this works much better, here some 
Carbons are off! In particular, atoms which are not directly bonded to 
large charge sinks (like S, N) deviate from my expected charges. I use 
CAMB3LYP as the XC, but I am unsure if I use it correctly. I looked at 
previous discussions for the use of CAMB3LYP, but I would be happy if 
anyone could confirm whether my approach is valid!

Attached are the script for the geometry optimization and the script for 
the single point calculation where I determine the RESP charges using 
REPEAT. I also provide the resulting output file for the charges and the 
"target" charges from gamess and my Basis/Potential files.

I would like to understand if this is a fitting issue, a basisset/potential 
issue or something in between. There are lots of options to turn on/off in 
cp2k and maybe I lack a crucial ingredient for RESP calculations. Maybe 
dispersion? How would I implement that? Any advice is appreciated. 

Thank You in advance. Sincerely, 
Andreas Doell

 

-- 
You received this message because you are subscribed to the Google Groups "cp2k" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cp2k+unsubscribe at googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/cp2k/52edb18a-8359-418e-b76b-2f78d2a3bfe5n%40googlegroups.com.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20250422/7d67c53f/attachment-0001.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: mol_geo.inp
Type: chemical/x-gamess-input
Size: 1968 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20250422/7d67c53f/attachment-0002.inp>
-------------- next part --------------
1   C   -0.089710
2   C   -0.031100
3   C    0.152810
4   C   -0.089710
5   C   -0.031100
6   C    0.152810
7   S   -0.245952
8   S   -0.245952
9   N   -0.739493
10  N   -0.739493
11  H    0.325614
12  H    0.325614
13  H    0.177200
14  H    0.125017
15  H    0.177200
16  H    0.325614
17  H    0.325614
18  H    0.125017
-------------- next part --------------
A non-text attachment was scrubbed...
Name: geo_opt.dat
Type: application/octet-stream
Size: 767694 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20250422/7d67c53f/attachment-0004.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: mol_repeat.inp
Type: chemical/x-gamess-input
Size: 3673 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20250422/7d67c53f/attachment-0003.inp>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: BASIS_SET
Type: application/octet-stream
Size: 19973 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20250422/7d67c53f/attachment-0005.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: charges_repeat.dat
Type: application/octet-stream
Size: 97336 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20250422/7d67c53f/attachment-0006.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: POTENTIAL_SET
Type: application/octet-stream
Size: 4963 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20250422/7d67c53f/attachment-0007.obj>