[gmx-users] Virtual Sites

[Brad Van Oosten]

I am trying to add virtual sites to a simulation with no mass or charge, just
to make tracking the center of mass of groups later easier later on.  

However, I keep getting the warning "The mass of a vsiten constructing atom
is <= 0" when i run grompp.

Here's the section of my .itp file where i have defined them:

[ atoms ]
;   nr       type  resnr residue  atom   cgnr     charge       mass  typeB   
chargeB      massB
; residue   1 CHX rtp CHX  q  0.0
     1       CLAL      1    CHX    CL1      1     -0.151     35.453   ; qtot
-0.151
.
.
.
.

    63         CA      1    CHX    CZ2     63      0.083     12.011   ; qtot
0.144
    64       CLAL      1    CHX    CL2     64     -0.144     35.453   ; qtot
0
    65       MCH3      1    CHX     V1     65          0          0   ; 
    66       MCH3      1    CHX     V2     66          0          0   ; 
    67       MCH3      1    CHX     V3     67          0          0   ; 
    68       MCH3      1    CHX     V4     68          0          0   ; 
    69       MCH3      1    CHX     V5     69          0          0   ; 
    70       MCH3      1    CHX     V6     70          0          0   ; 
    71       MCH3      1    CHX     V7     71          0          0   ; 
    72       MCH3      1    CHX     V8     72          0          0   ; 
    73       MCH3      1    CHX     V9     73          0          0   ; 
    74       MCH3      1    CHX    V10     74          0          0   ; 
    75       MCH3      1    CHX    V11     75          0          0   ;
    76       MCH3      1    CHX    V12     76          0          0   ;

[virtual_sitesn]
    65  2 	8 9 10 11 
    66  2 	2 3 6 7 
    67  2 	1 4 5 12 13
    68  2 	14 15 16 17 18
    69  2 	19 20 21 22 23
    70  2 	24 25 26 27 28 29 30 31 32
    71  2 	33 34 35 36 37 38 39 40 41
    72  2 	49 50 51 52 53
    73  2 	44 45 46 47 48
    74  2 	42 43 54 57 58
    75  2 	55 56 59 60
    76  2 	61 62 63 64


Am I defining something wrong here?

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