[gmx-users] free energy error

[aneamtu at iasi.mednet.ro]

Dear GMX users,

I try to simulate using free energy perturbation two
polymer systems. One of the polymers can be obtained
from the other one by removing some atoms from the
sidechains. I want to calculate the free energy
difference between the two systems. I added at the end
of the lines corresponding to the atoms I want to
"dissapear"  the new particle type, charge and mass:

...........
...........
24  CR61 3  ST  C8  3   0     13.019
25  CH2  4  GMA C1  4   0     14.027
26  CH1  4  GMA C2  4   0     13.019
27  C    4  GMA C3  4  0.5    12.011   C        0.530
28  O    4  GMA O4  4 -0.38   15.9994  O       -0.380
29  OS   4  GMA O5  4 -0.26   15.9994  OS      -0.150
30  CS2  4  GMA C6  4  0.2    14.027   CS2F     0.0
31  CS1  4  GMA C7  4  0.12   13.019   CS1F     0.0
32  CS2  4  GMA C8  4  0.12   14.027   CS2F     0.0
33  OS   4  GMA O9  4 -0.3    15.9994  OSF      0.0
34  CH3  4  GMA C10 4   0     15.035
35  CH2  5  ST  C1  5   0     14.027
............
............

I defined the atom types CS2F, CS1F, OSF with 0.0 vdW
parameters and all the bonded parameters in a separate
".itp" file and included it in topology.

When I run grompp program everything is OK, but when I
run mdrun it stops with the following error message:

"Fatal error:Force field inconsistency: 1-4 interaction
parameters for atoms 25-29 not the same as for other
atoms with the same atom type"

Can anyone tell me what this means? If I remove the
ending part of the lines 30, 31,32, 33 everything is OK
(but in this way I cannot usse free enrgy perturbation).
I use LINCS constraints on all the bonds.

Thank you,
Andrei