Coarse Grained model of RTIL in Examples\PACKAGES\electrode\ graph-il directory

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1

Greetings everyone,
I was looking for a simulation incorporating the coarse-grained model of Ionic Liquid (IL) and found example input data file and script in Examples\PACKAGES\electrode\graph-il folder.
In the input data file the IL is represented by a four-site model described in this paper: https://doi.org/10.1021/jp108179n

The masses and Lennard-Jones parameters are as expected in agreement with the paper but I am having difficulty understanding the following lines from the input file:

Bond Coeffs # harmonic

1 200 2.7076
2 200 3.8213

Angle Coeffs # harmonic

1 200 116.035

I could not find the parameters corresponding to the bond and angle coefficients in the above mentioned paper. I also did not find any other reference in the input file to look into.

So my question is how does one determine these parameters?

[PS: I understand the length and angle value can be calculated from atom coordinates. But what about the K parameters which are set to 200?]

2

The bond and angle parameters have to be set to something*, and those numbers convey that we want those to be stiff bonds and angles.

In practice this force field is only used with rigidified cations (SHAKE – see the accompanying input files in the folder) so the values are irrelevant during production. Also, there was a time when fix shake was not allowed during minimisation, and these parameters were used to keep the cations almost rigid during minimisation.

*Maybe not if the zero styles are used, but I haven’t played around with those much.

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