[gmx-users] opls parameters

[Mark Abraham]

> Sorry i'm probably being a bit slow, but i can't see where the "bond-type"
> atom names/types don't correspond with the opls-xxx names from the
> ffoplsbon.atp and ffoplsbon.rtp files for use with the ffoplsbon.itp file
> names.

The header for ffoplsaanb.itp is

[ atomtypes ]
; full atom descriptions are available in ffoplsaa.atp
; name  bond_type    mass    charge   ptype          sigma      epsilon
 opls_001   C   6      12.01100     0.500       A    3.75000e-01 
4.39320e-01 ; SIG
 opls_002   O   8      15.99940    -0.500       A    2.96000e-01 
8.78640e-01 ; SIG
 opls_003   N   7      14.00670    -0.570       A    3.25000e-01 
7.11280e-01 ; SIG
 opls_004   H   1       1.00800     0.370       A    0.00000e+00  0.00000e+00
 opls_005   C2  6      14.02700     0.200       A    3.80000e-01 
4.93712e-01 ; SIG

The header for ffoplsaa.atp is

 opls_001   12.01100  ;
 opls_002   15.99940  ;
 opls_003   14.00670  ;
 opls_004    1.00800  ;
 opls_005   14.02700  ;

So evidently opls_005 is a nitrogen atom... so what's with the "C2  6"?
Further, there is no bonded interaction in ffoplsaa.rtp for "C2", but
there is C_2... So I really don't understand what is going on.

Mark