# Minimum (non)working example of fix addforce parallel problem boundary p p f units metal atom_style atomic lattice fcc 7.500 region superbox block -30.0 30.0 -30.0 30.0 0.0 500.0 units box create_box 1 superbox compute avgz all reduce ave z thermo 100 variable z_0 equal 80.0 region init_atoms block -30.0 30.0 -30.0 30.0 60.0 90.0 units box create_atoms 1 region init_atoms mass 1 39.948 pair_style lj/cut 15.0000 pair_coeff * * 0.0103235642 3.405 neigh_modify every 2 delay 0 check yes one 5000 page 50000 fix ref all wall/reflect zlo EDGE zhi EDGE fix nvt all nvt temp 298.0 298.0 0.061 velocity all create 298.0 234324 dist gaussian mom yes rot yes variable umbrella_force atom -0.05*(c_avgz-${z_0}) fix umbrella_test all addforce 0.0 0.0 v_umbrella_force #<---- this line causes the problem thermo_style custom step v_z_0 c_avgz temp pe timestep 0.001 run 2000