Hi Rich,
In the manual compute page says "Thermodynamic output <http://*lammps.sandia.gov/doc/thermo_style.html> will normalize extensive values by the number of atoms in the system, depending on the "thermo_modify norm" setting. It will not normalize intensive values."
When you go to thermo_modify page, it says
"The option defaults are lost = error, norm = yes for unit style of /lj/, norm = no for unit style of /real/ and /metal/, flush = no, temp/press = compute IDs defined by thermo_style."
I hope this helps.
Hello,
When using a potential with LJ units, it appears that the
potential energy and kinetic energies found via a compute (i.e.
compute 1 all pe) are not extensive and instead are normalized by
the total number of atoms in the system. For example, if I compare
two fcc systems, with the same 1.0 density, but different numbers
of atoms, I find (both input scripts attached):
_*500 atoms, rho = 1.0, fcc, LJ/cut*_
pe ke vol Press
-7.761588e+00 1.497000e+00 5.000000e+02 -2.395575e+00
_*4000 atoms*__*, rho = 1.0, fcc, LJ/cut*_
pe ke vol Press
-7.761588e+00 1.499625e+00 4.000000e+03 -2.393825e+00
I am confused because I can do the same procedure with an EAM
potential and the compute is extensive. I assume that I have just
missed something or made a silly mistake. Can someone show me
where I am going wrong?
Thanks,
Richard
--
/Richard E. Baumer
PhD Candidate
MIT Department of Materials Science and Engineering
2010 //LLNL //CCMS Summer Institute Participant/
# 3d Lennard-Jones melt
units lj
atom_style atomic
lattice fcc 1.0
region box block 0.0 10.0 0.0 10.0 0.0 10.0
create_box 1 box
create_atoms 1 box
mass 1 1.0
velocity all create 1.0 87287
pair_style lj/cut 2.5
pair_coeff 1 1 1.0 1.0 2.5
neighbor 0.3 bin
neigh_modify every 1 delay 0 check no
thermo_style custom step etotal pe ke temp vol press
thermo_modify format float %15.6e
thermo 1
run 1
# 3d Lennard-Jones melt
units lj
atom_style atomic
lattice fcc 1.0
region box block 0.0 5.0 0.0 5.0 0.0 5.0
create_box 1 box
create_atoms 1 box
mass 1 1.0
velocity all create 1.0 87287
pair_style lj/cut 2.5
pair_coeff 1 1 1.0 1.0 2.5
neighbor 0.3 bin
neigh_modify every 1 delay 0 check no
thermo_style custom step etotal pe ke temp vol press
thermo_modify format float %15.6e
thermo 1
run 1
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