I am trying to use Tersoff potential for a simulation. The documentation
for Tersoff in the LAMMPS manual (manual dated 22 Jan, 2008) says that it
doesnt support stress/atom, energy/atom calculations. (pg 427) while at
the same time, the restrictions section in the documentation for compute
stress/atom command (pg 147) lists only airebo, meam and TIP4P as styles
which doesnt support it.
Is there an inconsistency? Can any one clarify?
Please see the 23 Jan 2008 bug fix:
"Updated the doc pages for the various pair styles to reflect that all
of them can now tally per-atom energy and stress so that they can be
used with the compute pe/atom and compute stress/atom commands."
Also, i am a bit confused about the units. I am using metal style units
in my simulation. Can anyone confirm the unit of the numbers computed
using compute stress/atom command. As far as i understand it should be in
eV for metal style.
"Note that as defined in the formula, per-atom stress is the negative
of the per-atom pressure tensor. It is also really a stress-volume
formulation, meaning the computed quantity is in units of
pressure-volume. It would need to be divided by a per-atom volume to
have units of stress (pressure), but an individual atom's volume is
not easy to compute in a deformed solid or a liquid. Thus, if the
diagonal components of the per-atom stress tensor are summed for all
atoms in the system and the sum is divided by 3V, where V is the
volume of the system, the result should be -P, where P is the total
pressure of the system. "
"For style metal, these are the units:
distance = Angstroms
time = picoseconds
mass = grams/mole
energy = eV
velocity = Angstroms/picosecond
force = eV/Angstrom
temperature = degrees K
pressure = bars
charge = multiple of electron charge (+1.0 is a proton)
dipole = charge*Angstroms
electric field = volts/Angstrom "
So pressure-volume units for style metal are bars*angs^3.