Missing dihedral OPLS-aa

EMC
1

Hello,

I am building cis-polybutadiene and was missing a torsion parameter in the opls-aa.prm for cm-ct-ct-cm (=CH-CH2-CH2-CH=)
Following the paper of Fröhlich 2013 (https://onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1002%2Fmats.201300103&file=mats201300103-sm-0001-SuppTables.pdf), I suggest adding this line to file field/opls/2012/opls-aa.prm:
cm ct ct cm 1.3 1 0 -0.05 2 0 0.2 3 0

Also, using the OPLS-UA is not preserving the stereochemistry of cis-butadiene even though I put SMILES code “*C/C=C\C*”, only OPLS-AA is preserving. Is there any torsion parameters missing in OPLS-UA too ?

Best,

Eddy BARRAUD

2

I am also modeling styrene butadiene rubber, and OPLS-aa 2012 is missing the definition of styrene cycles. If I try the OPLS-aa 2024 then it is missing torsion parameters:
Warning: no torsion coefficients found for [c4:c4:c3=:h1=].
Warning: no torsion coefficients found for [c3a:c4:c4:c3=].
Warning: no torsion coefficients found for [c3=:c4:c4:c3=].