Test particle insertion of multi-site test particles

User discussions
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1

GROMACS version: 5.0.7
GROMACS modification: No

Hi all,

I am wondering whether it is possible to perform test particle insertion of a multi-site model that incorporates charges. It seems that GROMACS’s reference manual is not very extended regarding this topic.

In our case; we’d like to use insert an oxygen molecule represented by a three-site model mimicking a quadrupole. The force field used is the TraPPE force field by Siepmann which implements two sites with negative charge -q and a virtual site with charge +2q. However, upon running I get:

“Fatal error:
The molecule to insert can not consist of multiple charge groups.
Make it a single charge group.”

In order to fix this I tried to implement the Bohn force field that uses two sites without any charges to represent the oxygen molecule. But unfortunately that resulted in the same error.

Any help is very much appreciated.

Best,

Stan

2

After fiddling around I found the solution. One should include all atoms in the same charge group by the cgnr parameter in the topology file and not by the charge parameter as I originally thought.

Best,

Stan