[gmx-users] Regarding the topology of triethylammonium ion generated using TPPMKTOP

[soumadwip ghosh]

Hi,
    I have recently used the TPPMKTOP topology builder for obtaining a
topology for triethylammonium ion consistent with OPLS-AA forcefield. To my
surprise, the total charge of the it comes out to be -0.400 while it should
be +1.000. I also generated a topology for acetate ions and it yields an
overall charge of -1.000 as expected. What is this anomaly for? Can you
please give me insights on how to assign correct charges to the atoms here?
Furthermore, the nitrogen atom is assigned to be secondary amine nitrogen
atom while in principle it should be a quarternary one. Is the topology
correct? I am uploading the PDB and the acetate.itp files in this mail.
Kindly help me out here. Has someone used the TPPMKTOP server before? Any
kind of insights would be hugely appreciated.

TEA pdb:
https://drive.google.com/file/d/0B7SBnQ5YXQSLRWxLdVhNbU9haVk/view?usp=sharing

TEA.itp:
https://drive.google.com/file/d/0B7SBnQ5YXQSLd2NDSnR3Rng4UjQ/view?usp=sharing

Thanks and regards,
Soumadwip Ghosh
Senior Research Fellow
Department of Chemistry
Indian Institute of Technology Bombay
India