imporved solution

docs/inputs/level1/breaking-a-carbon-nanotube/exercises/membrane/input.lammps

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+# Initialisation
+
+variable T equal 300
+
+units real
+atom_style molecular
+boundary p p p
+pair_style lj/cut 14
+
+bond_style harmonic
+angle_style harmonic
+dihedral_style opls
+improper_style harmonic
+
+special_bonds lj 0.0 0.0 0.5
+
+read_data cnt_molecular.data
+include parm.lammps
+
+change_box all x final -7 7 y final -7 7 # adjust the box size before replicating
+replicate 3 3 1 # replicate along x y to make 9 CNTs
+
+region center block INF INF 7 21 INF INF
+group CNT_center region center
+displace_atoms CNT_center move 7 0 0
+
+# let us first equilibrate using NPT anisotropic
+velocity all create ${T} 48455 mom yes rot yes
+fix mynpt all npt temp ${T} ${T} 100 x 1 1 1000 y 1 1 1000
+
+thermo 100
+
+timestep 1.0
+run 4000
+unfix mynpt
+reset_timestep 0
+
+change_box all triclinic
+
+dump mydmp all atom 500 dump.lammpstrj
+
+# use simple NVT
+fix mynvt all nvt temp ${T} ${T} 100
+
+# deform the box progressively 
+fix muyef all deform 1 xy erate 5e-5
+
+run 20000
+
+

docs/inputs/level1/breaking-a-carbon-nanotube/exercises/membrane/parm.lammps

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+pair_coeff 1 1 0.066047 3.4
+bond_coeff 1 469 1.4
+angle_coeff 1 63 120
+dihedral_coeff 1 0 7.25 0 0
+improper_coeff 1 5 180