[gmx-users] acpype generated different tip3p water paramters

[Yun Shi]

Hi all,

I just noted that the tip3p water converted from amber format to gromacs
format is

[ moleculetype ]
; molname       nrexcl ; TIP3P model
  WAT             2

[ atoms ]
;   nr   type  resnr residue  atom   cgnr     charge       mass
     1     OW      1     WAT     O      1     -0.834   16.00000
     2     HW      1     WAT    H1      1      0.417    1.00800
     3     HW      1     WAT    H2      1      0.417    1.00800

#ifdef FLEXIBLE
[ bonds ]
; i j   funct   length  force.c.
1   2   1   0.09572   462750.4 0.09572   462750.4
1   3   1   0.09572   462750.4 0.09572   462750.4

[ angles ]
; i j   k   funct   angle   force.c.
2   1   3   1   104.520    836.800  104.520    836.800
#else
[ settles ]
; i j   funct   length
1   1   0.09572 0.15139

[ exclusions ]
1   2   3
2   1   3
3   1   2
#endif


while in amber99sb.ff/tip3p.itp. it is

 moleculetype ]
; molname       nrexcl
SOL             2

[ atoms ]
; id  at type     res nr  res name  at name  cg nr  charge    mass
  1   OW          1       SOL       OW       1      -0.834    16.00000
  2   HW          1       SOL       HW1      1       0.417     1.00800
  3   HW          1       SOL       HW2      1       0.417     1.00800

#ifndef FLEXIBLE

[ settles ]
; OW    funct   doh     dhh
1       1       0.09572 0.15139

[ exclusions ]
1       2       3
2       1       3
3       1       2

#else

[ bonds ]
; i     j       funct   length  force_constant
1       2       1       0.09572 502416.0   0.09572        502416.0
1       3       1       0.09572 502416.0   0.09572        502416.0


[ angles ]
; i     j       k       funct   angle   force_constant
2       1       3       1       104.52  628.02      104.52  628.02

#endif

So it seems that the force_constants for O-H bond and H-O-H angle are
different? Does this mean amber and gromacs use different parameters for
tip3p water? or it's just acpype is not working right?

Thanks,
Yun
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-users/attachments/20110926/8eb2d4a8/attachment.html>