[gmx-developers] More OPLS-aa charge questions??

[Alan Chen]

I may be off my rocker but I can't figure out where some of the charges for 
HID and HIE
came from in the GROMACS implementation of OPLS-aa.  I suspect they may be 
based on Jorgensen's 1998 J Phys Chem B paper
(Vol 102 pp 8049-8059)  where they look at imidazole, but they don't match 
the atom type definitions GROMACS carried in  ffoplsaanb.itp.
Maybe one was updated but not the other by accident? Can anyone shed light 
on where the CB, NE2, HE1, and HE2 charges came from?

Thanks alot for your time.  In case people are wondering I've been using 
the GROMACS opls-aa entries to cross-check some
coding I'm doing for a monte-carlo package - I normally would never compare 
charge tables in my free time :-)

Alan Chen

 From ffoplsaa.rtp  GROMACS 3.2.1 release (similar for HISA entry as well)
-----------------------------------------------
[ HISB ]   ; HISE in OPLS terminology
  [ atoms ]
      N    opls_238   -0.500     1
      H    opls_241    0.300     1
     CA    opls_224B   0.140     1
     HA    opls_140    0.060     1
     CB    opls_505   -0.297     2
    HB1    opls_140    0.060     2
    HB2    opls_140    0.060     2
     CG    opls_507    0.504     3
    ND1    opls_511   -0.564     3
    CD2    opls_508   -0.261     4
    HD2    opls_146    0.183     4
    CE1    opls_506    0.182     5
    HE1    opls_146    0.098     5
    NE2    opls_503   -0.291     6
    HE2    opls_504    0.326     6
      C    opls_235    0.500     7
      O    opls_236   -0.500     7


atom definitions from ffoplsaanb.itp (which match Jorgensen 1996)
---------------------------------------------------------------
opls_146   HA      1.00800     0.115       A    2.42000e-01  1.25520e-01
opls_503   NA     14.00670    -0.570       A    3.25000e-01  7.11280e-01
opls_505   CT     12.01100    -0.005       A    3.50000e-01  2.76144e-01
opls_504   H       1.00800     0.420       A    0.00000e+00  0.00000e+00