Dear all LAMMPS users & developers.
First of all, I wish to send a gratitude to developers for sharing this nice molecular dynamics
I like to discuss about an anomalous result that I found recently.
I typically do ‘bulk’ things, especially crystalline or liquid Si with the Tersoff potential
by using LAMMPS.
There is no problem at all about bulk things, but recently I found something weird about
Si nano-wire simulations (of course, with the Tersoff potential.).
What I found is that some atoms nearby in the surface of a nano-wire have more stable
potential energy values than the energy value of the ground-state of cubic diamond.
A value is little different with respect of a postion, but the difference is quite huge, for example,
the energy value of cubic diamond; E_cd = -4.63 eV, but some atoms in the nano-wire
has -4.71 eV.
At first, I thought this is due to a characteristic of the potential so I made a custom code to
analyze this phenomenon but only found the discrepancy between my code and LAMMPS
(a result of my code does not show such phenomenon.).
A next thing that I did is checking energy of a single isolated tetrahedron by LAMMPS
(molecular statics). Bond-angles and pair lengths are same as cubic diamond,
therefore atoms in the center of tetrahedron must have an energy value which is identical to
the value the cubic diamond. Nonetheless, it turned out that the center atom has a one-step
lower energy (-4.96 eV).
With the indentical LAMMPS scripts, the Stillinger-Weber and MEAM potential do not show
I tested in two different LAMMPS version: 31Mar17 and 4Jan19.
The Tersoff potential that I used is Si© type in Physical Review B, vol 38, number 14 (1988).
I included my graphical summary pdf file and LAMMPS scripts with this e-mail.
Any comment about this problem will be helpful for me, personally I looked through
‘Tersoff.cpp & Tersoff.h’. The code itself seems fine but I suspect ev_tally() might be
the reason of this problem.
Si_tetrahedron_isolated.txt (341 Bytes)
Si89.tersoff (1.84 KB)
test.txt (1.57 KB)
anomaly.pdf (204 KB)