I am simulating a graphene model and found this error: Too many neighbor bins.
Suggest me some way to resolve this error.
Probably your initial structure is not well defined. Try visualising the data file (with Ovito or VMD) or dump a trajectory in your favourite format.
sudo suggest works better 
When reporting problems, please always report which LAMMPS version you are using and what platform you are running on. It also is often very helpful to see your input and a chunk of lines from the output before and including the full error message.
This means that either your simulation box is or has become too large or that your cutoff is too short.
Either way, there is something not quite right in your input or your simulation setup, but what it is requires to see it.
Here is my input script. Please suggest me some changes
units metal
atom_style atomic
dimension 3
boundary p p f
###################################VARIABLES#######################################
variable latparam equal 2.46
variable material string C
####################################ATOM DEFINITION################################
lattice hcp {latparam}
region whole block 0 120 0 120 0 120
create_box 1 whole
lattice hcp {latparam} orient x 1 0 0 orient y 0 1 0 orient z 0 0 1
create_atoms 1 region whole
mass 1 12.011
#set timestep
reset_timestep 0
timestep 0.1
pair_style airebo 1.0
pair_coeff * * CH.airebo C
delete_atoms overlap 0.1 all all
#Fixing a soft repulsive wall
fix wallhi all wall/harmonic xhi EDGE 80.0 80.0 40.0 units box
#Energy minimization
minimize 1e-14 1e-14 10000 10000
thermo 500
thermo_style custom step press pxx pyy pzz pe temp
velocity all create 300 12345 mom yes rot no
fix 1 all npt temp 300 300 1 iso 0 0 1 drag 1
run 200
unfix 1
#MSST fix
fix 2 all msst x 1000 q 500 v0 24000 e0 -1037.2288
variable dhug equal f_msst[1]
variable dray equal f_msst[2]
variable lgr_vel equal f_msst[3]
variable lgr_pos equal f_msst[4]
compute 2 all_MSST_temp all temp
compute 2 all_MSST_press all pressure
compute 2 all_MSST_pe all pe
thermo_style custom step temp ke pe lx ly lz pxx pyy pzz etotal econserve v_dhug v_dray v_lgr_vel v_lgr_pos f_msst
#Use custom dump for Ovito output
dump 1 all custom 250 dump_C_equil*.lammpstrj id x y z c_peratom fx fy fz c_virial[1] c_virial[2] c_virial[3] c_virial[4] c_virial[5] c_virial[6]
#Run for 50ps
run 500
now I am getting error that you cannot use npt ensemble in nonperiodic boundary…Suggest me which ensemble would work with non periodic boundary?
It seems that you are discovering MD by trial and error.
Anyway, what you want to achieve can be done with something like:
boundary p p p
[...]
fix NPT2D all npt temp 300. 300. $(100*dt) x 0 0 $(1000*dt) y 0 0 $(1000*dt)
Thanks a lot. But will you please explain me the significance of this code which you have sent? I need to understand it…
I think you misunderstand the use of this forum.
If your goal is to do science (graduate / get a PhD / write a scientific article), then relying on the advice of some random guy from a forum is hardly a good idea. Ask your mentor, find a relevant course at your local institution, or study from a textbook. There is plenty to choose from.
If your goal is to learn LAMMPS, then start by reading the manual. I know it is intimidating, with its almost 3000 pages. But you don’t have to read it all: start from one of the examples and read the documentation for each command. It’s all there. I personally always use the PDF, as it has a very handy clickable outline (plus a much lower carbon footprint than searching the manual through Google).
A brief comment on the snippet I wrote, taken straight from the Manual™:
The barostat can be coupled to the overall box volume, or to individual dimensions, including the xy, xz and yz tilt dimensions.
[cut]
The target pressures for each of the 6 components of the stress tensor can be specified independently via the x, y, z, xy, xz, yz keywords, which correspond to the 6 simulation box dimensions.
I have also use immediate variables to set the coupling constant to the recommended values of 100x and 1000x the timestep for the thermostat and barostat, respectively. The z dimension is kept fixed, but the pressure requires the box to be periodic in all dimensions. This requirement is not stated very clearly in the manual, but the error message you got is self-explanatory.
PS Good practices:
