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I want to perform some MD including Li+ ions. Specifically I am interested in Li-TFSI (aka Lithium bis(trifluoromethanesulfonyl)imide).

I tested both the ATB repository and LigParGen and neither can provide Li parameters.

The calculation 1273328 on ATB fails since Atom type 'LI' not currently supported by the ATB. enter image description here On LigParGen there is no Lithium allowed export BOSSdir=/var/www/html/ligpargen/apps/boss-4.9;/var/www/html/ligpargen/apps/anaconda2/bin/python2.7 /var/www/html/ligpargen/apps/ligpargenCode/Converter.py -s '[Li]' -r UNK -o 0 -c 0 > /tmp/errorServer.log

I tried two smiles as FC(F)(F)S(=O)(=O)N([Li])S(=O)(=O)C(F)(F)F and [Li+][N-](S(=[O-])(=[O-])C(F)(F)F)S(=[O-])(=[O-])C(F)(F)F

enter image description here enter image description here

I tried also to search the Li related parameters into OPLS from Yale or in abmer but I couldn't find much. In amber I tried to run antechamber on my Li-TFSI.pdb input file, obtaining this:

Warning: Unusual element (Li) for atom (ID: 16, Name: Li).
/Users/marcodigennaro/miniconda3/envs/lammps/bin/wrapped_progs/antechamber: Fatal Error!
GAFF does not have sufficient parameters for molecules having unusual
       elements (those other than H,C,N,O,S,P and halogens).

Question: Do you know any Li parametrization to add to these force fields?

Many thanks

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  • $\begingroup$ Just a hunch. In the error, it shows LI instead of Li. Could the Lithium atom be misspelt as LI in any of the input files perhaps? $\endgroup$ Jun 17, 2023 at 10:12
  • $\begingroup$ I don't think this is the case. I submitted CH2O3Li as a test and receive the same error. $\endgroup$ Jun 19, 2023 at 7:27
  • $\begingroup$ Also LigParGen has the same problem. There is no Lithium allowed ``` export BOSSdir=/var/www/html/ligpargen/apps/boss-4.9;/var/www/html/ligpargen/apps/anaconda2/bin/python2.7 /var/www/html/ligpargen/apps/ligpargenCode/Converter.py -s '[Li]' -r UNK -o 0 -c 0 > /tmp/errorServer.log ``` $\endgroup$ Jun 27, 2023 at 7:31
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    $\begingroup$ @MarcoDiGennaro, if it is suitable, you can explore other force field repositories to see if they have the required parameters. Some popular force field repositories include CHARMM, AMBER, and OPLS. Check their documentation or literature references to see if Li+ parameters are available. for instance, here you can refer to AMBER project ambermd.org/AmberModels_ions.php I believe they have the thing you are looking for. $\endgroup$ Nov 18, 2023 at 7:24
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    $\begingroup$ @MarcoDiGennaro Moreover, on ATB you may try to transfer force field parameters from similar atoms or ions to Li+. For example, you could consider using parameters for sodium (Na+) or potassium (K+), which have similar electronic structures and properties to Li+. However, this approach may not provide accurate results, especially for properties specific to Li+. Regards~ $\endgroup$ Nov 18, 2023 at 7:24

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So far, I could find these three sources for parameters for a LJ parametrisation of Li

Ref epsilon (kJ/mol) sigma (Ang)
1 CL&P for ionic liquids 0.07648 2.126
2 Wu & Wick Macrom. 2010 1.67470 1.400
3 Starovoytov J. Phys. Chem. B 2021 0.10500 2.000

These results are different since they have been parametrized to optimize different properties and show that there is not a unique way to parametrize this element. Besides the large variability, a posteriori, I can see how transport quantity are not largely modified by the specific value.

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