[gmx-users] Virtual site and constraints

[Нилов Дмитрий]

Hello!
I would like to involve formate molecule (HCOO-)in my dynamics, but I have the problem when I use virtual site (type 3fd)for it.

When I run grompp for single formate molecule, it`s ok.
But after solvating in bath of solvent (tip3p) grompp runs with error:

Cleaning up constraints and constant bonded interactions with virtual sites
Removed      1     Proper Dih.s with virtual sites,     0 left
Converted    1      Constraints with virtual sites to connections,     2 left
ERROR: Cannot have constraint (5-1) with virtual site (1)
ERROR: Cannot have constraint (8-1) with virtual site (1)
ERROR: Cannot have constraint (11-1) with virtual site (1)
ERROR: Cannot have constraint (14-1) with virtual site (1)
..........................................
ERROR: Cannot have constraint (3101-1) with virtual site (1)
ERROR: Cannot have constraint (3104-1) with virtual site (1)
-------------------------------------------------------
Program grompp, VERSION 3.3.1
Source code file: vsite_parm.c, line: 686

Fatal error:
There were 1034 virtual sites involved in constraints
-------------------------------------------------------

And 1034 is number of water molecules. In my mdp file the line that corresponds to constraints is
"constraints = none". This is my topology:

#include "ffoplsaa.itp"

[ moleculetype ]
; Name            nrexcl
FMT                 3

[ atoms ]
;   nr       type  resnr residue  atom   cgnr     charge       mass  
     1   opls_279      1    FMT      H      1       0.22          0   ; qtot 0.22
     2   opls_271      1    FMT      C      1       0.58     13.019   ; qtot 0.8
     3   opls_272      1    FMT     O1      1       -0.9    15.9994   ; qtot -0.1
     4   opls_272      1    FMT     O2      1       -0.9    15.9994   ; qtot -1

[ bonds ]
;  ai    aj funct            c0            c1            c2            c3
    1     2     1 
    2     3     1 
    2     4     1 

[ angles ]
;  ai    aj    ak funct            c0            c1            c2            c3
    1     2     3     1    ang_FMT_H_C_O1
    1     2     4     1    ang_FMT_H_C_O2
    3     2     4     1    ang_FMT_O1_C_O2

[ dihedrals ]
;  ai    aj    ak    al funct            c0            c1            c2            c3
    1     3     2     4     1    improper_O_C_X_Y

[ virtual_sites3 ]
;  ai    aj    ak    al funct            c0            c1
    1     2     3     4     2 

; Include water topology
#include "tip3p.itp"

[ system ]
; Name
FMT in water

[ molecules ]
; Compound        #mols
FMT                 1
SOL              1034


Could You help me to solve this roblem!
Thanks!
_____________
Dmitri Nilov