Homec4science
Diffusion lammps (lammm-devel) Browse

lammps/doc/pair_lj_cubic.txt
4f41208c12c0lammm-devel

Last Change
Raw File

pair_lj_cubic.txt
View Options

"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
pair_style lj/cubic command :h3
[Syntax:]
pair_style lj/cubic :pre
[Examples:]
pair_style lj/cubic
pair_coeff * * 1.0 0.8908987 :pre
[Description:]
The {lj/cubic} style computes a truncated LJ interaction potential whose
energy and force are continuous everywhere.
Inside the inflection point the interaction is identical to the
standard 12/6 "Lennard-Jones"_pair_lj.html potential.
The LJ function outside the inflection point is replaced
with a cubic function of distance. The energy, force, and second
derivative are continuous at the inflection point.
The cubic coefficient A3 is chosen so
that both energy and force go to zero at the cutoff distance.
Outside the cutoff distance the energy and force are zero.
:c,image(Eqs/pair_lj_cubic.jpg)
The location of the inflection point rs is defined
by the LJ diameter, rs/sigma = (26/7)^1/6. The cutoff distance
is defined by rc/rs = 67/48 or rc/sigma = 1.737....
The analytic expression for the
the cubic coefficient
A3*rmin^3/epsilon = 27.93... is given in the paper by
Holian and Ravelo "(Holian)"_#Holian.
This potential is commonly used to study the shock mechanics
of FCC solids, as in Ravelo et al. "(Ravelo)"_#Ravelo.
The following coefficients must be defined for each pair of atom
types via the "pair_coeff"_pair_coeff.html command as in the example
above, or in the data file or restart files read by the
"read_data"_read_data.html or "read_restart"_read_restart.html
commands, or by mixing as described below:
epsilon (energy units)
sigma (distance units) :ul
Note that sigma is defined in the LJ formula as the zero-crossing
distance for the potential, not as the energy minimum, which
is located at rmin = 2^(1/6)*sigma. In the above example, sigma = 0.8908987,
so rmin = 1.
:line
[Mixing, shift, table, tail correction, restart, rRESPA info]:
For atom type pairs I,J and I != J, the epsilon and sigma coefficients
and cutoff distance for all of the lj/cut pair styles can be mixed.
The default mix value is {geometric}. See the "pair_modify" command
for details.
The lj/cubic pair style does not support the
"pair_modify"_pair_modify.html shift option,
since pair interaction is already smoothed to 0.0 at the
cutoff.
The "pair_modify"_pair_modify.html table option is not relevant
for this pair style.
The lj/cubic pair style does not support the
"pair_modify"_pair_modify.html tail option for adding long-range tail
corrections to energy and pressure, since there are no corrections for
a potential that goes to 0.0 at the cutoff.
The lj/cubic pair style writes its information to "binary
restart files"_restart.html, so pair_style and pair_coeff commands do
not need to be specified in an input script that reads a restart file.
The lj/cubic pair style can only be used via the {pair}
keyword of the "run_style respa"_run_style.html command. It does not
support the {inner}, {middle}, {outer} keywords.
:line
[Restrictions:] none
[Related commands:]
"pair_coeff"_pair_coeff.html
[Default:] none
:line
:link(Holian)
[(Holian)] Holian and Ravelo, Phys Rev B, 51, 11275 (1995).
:link(Ravelo)
[(Ravelo)] Ravelo, Holian, Germann and Lomdahl, Phys Rev B, 70, 014103 (2004).
c4science · Help