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lammps/test/02_commands/in.compute_force-003
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in.compute_force-003
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units real
atom_style full
timer off
read_data spce.data
pair_style lj/cut/coul/long 12.0 12.0
kspace_style pppm 1.0e-4
pair_coeff 1 1 0.15535 3.166
pair_coeff * 2 0.0000 0.0000
bond_style harmonic
angle_style harmonic
dihedral_style none
improper_style none
bond_coeff 1 1000.00 1.000
angle_coeff 1 100.0 109.47
special_bonds lj/coul 0.0 0.0 1.0
neighbor 2.0 bin
fix 1 all shake 0.0001 20 0 b 1 a 1
fix 2 all nvt temp 300.0 300.0 100.0
group one molecule 1 2
# the following section shows equivalences between using the pe/tally compute and other computes and thermo keywords
# compute pairwise force between two molecules and everybody
compute fpa one group/group all pair yes kspace no boundary no
# tally pairwise force between two molecules and the all molecules
compute c1 one force/tally all
# tally the force of all with all (should be zero)
compute c3 all force/tally all
compute c2 all force/tally all
# collect per atom data. only reduce over the first group.
compute one one reduce sum c_c1[1] c_c1[2] c_c1[3]
compute red all reduce sum c_c2[1] c_c2[2] c_c2[3]
# determine magnitude of force
variable fpa equal sqrt(c_fpa[1]*c_fpa[1]+c_fpa[2]*c_fpa[2]+c_fpa[3]*c_fpa[3])
variable for equal sqrt(c_one[1]*c_one[1]+c_one[2]*c_one[2]+c_one[3]*c_one[3])
# round to 10**-10 absolute precision.
variable ref equal round(1e10*sqrt(c_red[1]*c_red[1]+c_red[2]*c_red[2]+c_red[3]*c_red[3]))*1e-10
variable all equal round(1e10*c_c2)*1e-10
velocity all create 300 432567 dist uniform
timestep 2.0
# v_fpa and v_for and c_c1, c_fpa[] and c_one[] should all each have the same value. v_ref and c_c2 should be zero
thermo_style custom step v_fpa v_for c_c1 c_fpa[1] c_one[1] c_fpa[2] c_one[2] c_fpa[3] c_one[3] v_ref v_all
thermo 10
run 0 post no
uncompute c3
info all
run 50
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