[gmx-users] Potassium ions in OPLS-AA (II)

[Lieven Buts]

I have just (re)discovered an updated "ions.itp"
(posted by David van der Spoel) which defines
residue types [ NA+ ] and [ K+ ]. These work
fine, but I still don't understand why the [ K ]
definition in 3.1.4 ffoplsaa.rtp doesn't work.

ions.itp (updated):
------------------
#ifdef _FF_OPLS

...

[ moleculetype ]
; molname       nrexcl
NA+             1

[ atoms ]
; id    at type         res nr  residu name     at name  cg nr  charge  
mass
1       opls_407        1       NA+             NA       1      1      
22.98977

[ moleculetype ]
; molname       nrexcl
K+              1

[ atoms ]
; id    at type         res nr  residu name     at name  cg nr  charge  
mass
1       opls_408        1       K+              K        1      1       
39.0983

...



ffoplsaa.rtp (3.1.4):
--------------------
...

[ NA ]
 [ atoms ]
    NA   opls_407   1.000     0 ; Jorgensen ion type would be opls_405

[ K ]
 [ atoms ]
    K    opls_408   1.000     0

...


-- 
Lieven Buts
Brussels Free University