dimension 3
units lj
boundary f f f

read_data msd.sphere.data
mass 1 1.0

pair_style none
atom_modify sort 0 1.0

variable R equal 8
fix step all nve/manifold/rattle 1e-4 4 sphere $R
fix temp all langevin 1.0 1.0 1.0 12321 gjf yes
velocity all create 1.0 1283
run 25000
compute dx2 all msd

variable D equal "1.0"
variable t equal time
variable my_msd equal "2*v_R*v_R*(1.0 - exp(-2*(v_t-125)*v_D/(v_R*v_R)) )"
variable msd equal c_dx2[4]

fix msd_out all print 250 "$t    ${msd}    ${my_msd}" file msd.sphere.dat screen no

thermo_style custom time step pe ke etotal temp c_dx2[4] v_my_msd
thermo 1000
run 25000