[lammps-users] Problem in treating fullerene(C60) as rigid body

Dear All:
          I am trying to simulate a system consisting of fullerene molecules
on heterogeneous silicon surface having defects using lammps. The
surface contains two types of silicon atoms, on the top of which
there are some fullerene molecules. The surface atoms are supposed to keep
frozen during simulation and fullerene molecules are treated as rigid body.
For the sake of simplicity, I have taken a
homogeneous silicon surface containing only one type of silicon
atoms and few fullerene molecules on the top.

units real
atom_style atomic
boundary p p p
read_data data.si
pair_style tersoff
pair_coeff * * SiC.tersoff Si C
velocity all create 300.0 352839
timestep 1.0
group clump1 id <> 1 3276
group c60 id <> 3277 4236
fix 1 clump1 recenter INIT INIT INIT units box
fix 2 c60 rigid molecule
#fix 2 c60 nve
#fix 2 c60 nvt 300.0 300.0 100.0
thermo 100
dump 1 all xyz 50 dump.c60
run 2000

#data file Si and C60

4236 atoms
2 atom types

-31.7 31.7 xlo xhi
-57.2 57.2 ylo yhi
-75.0 75.0 zlo zhi

Masses

  1 28.0000
  2 12.0000

Atoms

         atom-type x y z
    1 1 -31.1849995 31.1850204 3.0400000
  ----- --- ----- ---- ---
  3276 1 ---- ---- ----
  ----- --- ---- ---- ----
  3277 2 --- --- --
  ---- --- --- --- ---
  4236 2 --- -- --

then it is showing error: Must use a molecular atom style with fix rigid
molecule,
then I moved to "fix 2 c60 rigid single", then I found that all the
fullerene molecules are moving as a single body and silicon surface remain as
stationary. After that I changed atom_style to "atom_style molecular" along
with

the data file-
group c60 id <> 3277 4236
fix 1 clump1 recenter INIT INIT INIT units box
fix 2 c60 rigid molecule

and data file having format as given below

4236 atoms
2 atom types

-31.7 31.7 xlo xhi
-57.2 57.2 ylo yhi
-75.0 75.0 zlo zhi

Masses

  1 28.0000
  2 12.0000

Atoms

         molecule-tag atom-type x y z
    1 1 1 -31.1849995 31.1850204 3.0400000
  ----- --- ----- ---- ---
   3276 1 ---- ---- ---- -----

   --- ---- ---- ----

  3277 3277 2 --- --- --
  3278 3277 2
   --- -- --
  3335 3277 -- -- --- ------
  3336 3278 2 --

  --- --- --- ---
  4236 3293 2 --- -- --

In data file the charge(q) column is not undestood by in file, so I have not
given.
Here, the part of the first fullerene molecule although move but othere
fullerene molecules remain as stationary. But I need the surface should be
stationary and fullerene molecules should move as individual rigid body at
the desired temperature. Please suggest me the proper key words to make
fullerene as
rigid body or any way, also help me how to use tersoff potenatial for two
different type of Si atoms in the surface with the different degree of
interactions with the C atoms.

Thanking you,
With regards,

Malay Rana
  IITK