[gmx-users] how to keep nanotube cylindrical

[Za Pour]

Dear Justin
I appreciate for your reply.I used -maxwarn option because grompp gave me:
WARNING 1 [file ffbonded.itp, line 2705]:
  Overriding Bond parameters.

  old: 0.151 292880 0.151 292880 
  new: C   C  1   0.1418   478900
I guess I am not using improper in the topology file.my cnt.top file looks like:
; Include forcefield parameters
#include "./oplsaa.ff/forcefield.itp"

[ moleculetype ]
; Name            nrexcl
CNT                 3

[ atoms ]
;   nr       type  resnr residue  atom   cgnr     charge       mass  typeB    chargeB      massB
     1   opls_995      1    UNK      C      1          0     12.011   ; qtot 0
     2   opls_995      1    UNK      C      2          0     12.011   ; qtot 0
     3   opls_996      1    UNK      C      3          0     12.011   ; qtot 0
   ......
[ bonds ]
;  ai    aj funct            c0            c1            c2            c3
    1     2     1  1.420000e-01  4.789000e+05  1.420000e-01  4.789000e+05 
    1    73     1  1.420000e-01  4.789000e+05  1.420000e-01  4.789000e+05 
    2     4     1  1.420000e-01  4.789000e+05  1.420000e-01  4.789000e+05 
.....

[ pairs ]
;  ai    aj funct            c0            c1            c2            c3
    1     3     1 
    1     5     1 
    1    71     1
......

[ angles ]
;  ai    aj    ak funct            c0            c1            c2            c3
    2     1    73     1  1.180000e+02  5.622000e+02  1.180000e+02  5.622000e+02 
    1     2     4     1  1.190000e+02  5.622000e+02  1.190000e+02  5.622000e+02 
    4     3     9     1  1.200000e+02  5.622000e+02  1.200000e+02  5.622000e+02 
........

[ dihedrals ]
;  ai    aj    ak    al funct            c0            c1            c2            c3            c4            c5
   73     1     2     4     3  1.910000e+02  5.000000e+00  3.000000e+00  1.910000e+02  5.000000e+00  3.000000e+00 
    2     1    73    72     3  2.520000e+02  5.000000e+00  3.000000e+00  2.520000e+02  5.000000e+00  3.000000e+00 
    1     2     4     3     3  2.240000e+02  5.000000e+00  3.000000e+00  2.240000e+02  5.000000e+00  3.000000e+00 
   ........
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