Forcefield parameters addition for LiTFSI in opls-aa

EMC
1

I am trying to use the TFSI ion parameters from Lopez and Padua in OPLS-AA 2012. I have tried editing the opls-aa.define file, followed instructions from a previous topic (Oct 2023). I have tried both the emc_opls.pl and convert.sh scripts to create the opls-aa.prm files. It doesnt get updated, and there is no error either.

ITEM MASSES
#-----------TFSI ion---------------------------------

#type    mass      element  ncons   charge    comment

ct_6      12.011    C        4       0         # TFSI Carbon
f_6       18.998    F        1       0         # TFSI Fluorine
sy_6      32.060    S        4       0         # TFSI Sulfur
oy_6      15.999    O        1       0         # TFSI Oxygen
nt_6      14.007    N        2       0         # TFSI Nitrogen
#-----------TFSI ion---------------------------------
ITEM END
ITEM EXTRA

#index    basis    type     charge    comment

702.1      ct       ct_6      0.350    # TFSI Carbon
706.1      f        f_6      -0.160    # TFSI Fluorine
961.1      sy       sy_6      1.020    # TFSI Sulfur
964.1      oy       oy_6     -0.530    # TFSI Oxygen
752.1      nt       nt_6     -0.660    # TFSI Nitrogen

ITEM END
ITEM NONBOND

#type1   type2   sigma     epsilon

ct_6     ct_6   3.500     0.0660    # ct (Carbon)
f_6     f_6   2.950     0.0530    # f (Fluorine)
sy_6     sy_6   3.550     0.2500    # sy (Sulfur)
oy_6     oy_6   2.960     0.2100    # oy (Oxygen)
nt_6     nt_6   3.250     0.1700    # nt (Nitrogen)

ITEM END

ITEM BOND

ct_6     f_6    441.802   1.323    # ct - f (TFSI)
ct_6     sy_6    235.420   1.818    # ct - sy (TFSI)
sy_6     oy_6    637.069   1.442    # sy - oy (TFSI)
sy_6     nt_6    372.012   1.570    # sy - nt (TFSI)

ITEM END

ITEM ANGLE

f_6    ct_6  f_6    93.3317   107.1    # F-C-F (TFSI)
sy_6    ct_6  f_6    82.9349   111.8    # S-C-F (TFSI)
ct_6    sy_6  oy_6   103.9674   102.6    # C-S-O (TFSI)
oy_6    sy_6  oy_6   115.7982   118.5    # O-S-O (TFSI)
oy_6    sy_6  nt_6    94.2877   113.6    # O-S-N (TFSI)
ct_6    sy_6  nt_6    97.5143   100.2    # C-S-N (TFSI)
sy_6    nt_6  sy_6    80.1864   125.6    # S-N-S (TFSI)

ITEM END

ITEM TORSION

sy_6     nt_6   sy_6   ct_6   7.8329   1       0
sy_6     nt_6   sy_6   ct_6  -2.4904   2       0
sy_6     nt_6   sy_6   ct_6  -0.7636   3       0

f_6     ct_6   sy_6   nt_6   0.3159   3       0

f_6     ct_6   sy_6   oy_6   0.3468   3       0

sy_6     nt_6   sy_6   oy_6  -0.0036   3       0

ITEM END
ITEM RULES

702.1    [C](F)(F)(F)(S)
706.1    [F](C)
961.1    [S](=O)(=O)(N)(C)
964.1    [O](=S)
752.1    [N](S)(S)
ITEM END

I have tried putting the index and the type in precedence, i have tried adding [] to the first atom in rules, Im not sure how to solve this. I also tried with the old emc_opls.pl script

Please help, Im stuck.
Thank you

2

After 2 days of more head cracking, I was finally able to solve the issue. I realised the problems were in the index.serial assignment, and the equivalence declaration. Also, I was not aware I had to use tabs instead of spaces.:sweat_smile:

Thank you

3

Dear user,

I am happy to hear you were able to find the issues out by yourself. Unfortunately, the emc_opls.pl tool indeed expects tabs as separators in your define file. Would you be so kind and share your eventual solution with the rest of us? Thank you in advance!

4

Dear Veld,

Thank you for your reply

I have attached the opls-aa.define file.

I took the forcefields from the Lopez and Padua paper, but the use of tabs instead of spaces was pointed out by claude code. I have also attached a small guide document i made enlisting the help of claude, to enable me to add new parameters, without any other guidance. I hope this will help someone in a similar position as me.

Thank you for your responses to previous questions, that helped solve the issue.

EMC_OPLS-AA_Custom_FF_Guide.docx (23.1 KB)

opls-aa.define (28.3 KB)

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