dump custom / fx fy fz, wrong fx,fy,fz

Dear lammps users !

I have problem with the dump command. I get wrong fx, fy and fz
forces on atoms.
I tried different dump versions in my input file as follows:

units metal

boundary s s s

atom_style atomic

lattice custom 1.0 a1 1.625 -2.79 0.0 a2 1.625 2.79 0.0 a3 0.0 0.0 5.26 &
basis 0.33333333 0.66666667 0.0 basis 0.66666667 0.33333333 0.5

region 1 cylinder x 0. 0. 50. -150. 150. units box

create_box 2 1

create_atoms 1 region 1 basis 1 1 basis 2 1

lattice custom 1.0 a1 1.625 -2.79 0.0 a2 1.625 2.79 0.0 a3 0.0 0.0 5.26 &
basis 0.33333333 0.66666667 0.3748 basis 0.66666667 0.33333333 0.8748

create_atoms 2 region 1 basis 1 2 basis 2 2

mass 1 65.39
mass 2 15.999

pair_style tersoff

pair_coeff * * ZnO.tersoff Zn O

dump dumpXYZ all custom 1 force.xyz type x y z id fx fy fz

#dump coords all custom 1 force.xyz type x y z id fx fy fz

#dump e_data all custom 1 cyl_3nm_nw0.xyz type x y z id fx fy fz

run 0

none of them give correct fx,fy,fz values. I compared them with another
code in which I belive in, and I get too large forces with lammps.
T used units metal seems to be OK.
I have no idea what is wrong. I would like to get simply in eV/A the forces on each atoms. Could you help me please ?

Best regards, Peter Sule

Since the Tersoff potential in LAMMPS is widely used,
its very unlikely its forces are wrong. You'd have to provide
further evidence.

Steve

2011/4/11 Süle Péter <[email protected]>:

Dear Steve,

My dump file looks sg. like this:

type x y z id fx fy fz
2 -199.875 -12.09 -47.9986 131901 1.34329 0.69025 1.0591
2 -196.625 -12.09 -47.9986 131904 -9.13852e-15 -0.500787 0.862586
2 -193.375 -12.09 -47.9986 131909 -1.17613e-13 -0.500787 0.862586
2 -190.125 -12.09 -47.9986 131916 9.89382e-14 -0.500787 0.862586
2 -186.875 -12.09 -47.9986 131925 -2.16441e-14 -0.500787 0.862586
2 -183.625 -12.09 -47.9986 131935 -7.85309e-15 -0.500787 0.862586
2 -180.375 -12.09 -47.9986 131945 -1.17323e-13 -0.500787 0.862586
2 -177.125 -12.09 -47.9986 131955 1.32214e-13 -0.500787 0.862586
2 -173.875 -12.09 -47.9986 131965 5.07233e-15 -0.500787 0.862586
2 -170.625 -12.09 -47.9986 131975 -1.17613e-13 -0.500787 0.862586
2 -167.375 -12.09 -47.9986 131985 1.2736e-13 -0.500787 0.862586

or elsewhere in the file:

2 164.125 6.51 49.3114 264353 2.16493e-15 -0.00213823 -1.55912
2 167.375 6.51 49.3114 264359 0 -0.00213823 -1.55912
2 170.625 6.51 49.3114 264365 0 -0.00213823 -1.55912
2 173.875 6.51 49.3114 264371 0 -0.00213823 -1.55912
2 177.125 6.51 49.3114 264377 0 -0.00213823 -1.55912

You can see that fy and fz look strange. The same values occur.
If I sum up the forces for each coordinates, I get too large
for fy. It could be a unit problem or sg. else.

Peter

They do look strange - can you post a simple, small
example input and data file that reproduces it?

Steve

2011/4/11 Süle Péter <[email protected]>: