Add fix elstop to USER-MISC

"edpd/source"_fix_dpd_source.html,

"efield"_fix_efield.html,

"ehex"_fix_ehex.html,

"elstop"_fix_elstop.html,

"enforce2d (k)"_fix_enforce2d.html,

"eos/cv"_fix_eos_cv.html,

"eos/table"_fix_eos_table.html,

\documentclass[12pt]{article}

\begin{document}

$$ 

  {\vec F}_i = {\vec F}^{0}_i - \frac{{\vec v}_i}{\|\vec{v}_i\|}\cdot S_e

$$

\end{document}

"edpd/source"_fix_dpd_source.html -

"efield"_fix_efield.html - impose electric field on system

"ehex"_fix_ehex.html - enhanced heat exchange algorithm

"elstop"_fix_elstop.html - electronic stopping power as a friction force

"enforce2d"_fix_enforce2d.html - zero out z-dimension velocity and force

"eos/cv"_fix_eos_cv.html -

"eos/table"_fix_eos_table.html -

"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)

:link(ld,Manual.html)

:link(lc,Commands_all.html)

:line

fix elstop command :h3

[Syntax:]

fix ID group-ID elstop Ecut file keyword value ... :pre

ID, group-ID are documented in "fix"_fix.html command :ulb,l

elstop = style name of this fix command :l

Ecut = minimum kinetic energy for electronic stopping (energy units) :l

file = name of the file containing the electronic stopping power table :l

zero or more keyword/value pairs may be appended to args :l

keyword = {region} or {minneigh} :l

  {region} value = region-ID

    region-ID = region, whose atoms will be affected by this fix

  {minneigh} value = minneigh

    minneigh = minimum number of neighbors for atoms to have elstop applied :pre

:ule

[Examples:]

fix el all elstop 10.0 elstop-table.txt

fix el all elstop 10.0 elstop-table.txt minneigh 3

fix el mygroup elstop 1.0 elstop-table.txt region bulk :pre

[Description:]

This fix implements inelastic energy loss for fast projectiles in solids. It

applies a friction force to fast moving atoms to slow them down due to

"electronic stopping"_#elstopping (energy lost via electronic collisions per

unit of distance). This fix should be used for simulation of irradiation

damage or ion implantation, where the ions can lose noticeable amounts of

energy from electron excitations. If the electronic stopping power is not

considered, the simulated range of the ions can be severely overestimated

("Nordlund98"_#Nordlund98, "Nordlund95"_#Nordlund95).

The electronic stopping is implemented by applying a friction force

to each atom as:

:c,image(Eqs/fix_elstop.jpg)

where \(\vec\{F\}_i\) is the resulting total force on the atom. \(\vec\{F\}^0_i\)

is the original force applied to the atom, \(\vec\{v\}_i\) is its velocity and

\(S_e\) is the stopping power of the ion.

NOTE: In addition to electronic stopping, atomic cascades and irradiation

simulations require the use of an adaptive timestep (see

"fix dt/reset"_fix_dt_reset.html) and the repulsive ZBL potential (see

"ZBL"_pair_zbl.html potential) or similar. Without these settings the

interaction between the ion and the target atoms will be faulty. It is also

common to use in such simulations a thermostat ("fix_nvt"_fix_nh.html) in

the borders of the simulation cell.

NOTE: This fix removes energy from fast projectiles without depositing it as a

heat to the simulation cell. Such implementation might lead to the unphysical

results when the amount of energy deposited to the electronic system is large,

e.g. simulations of Swift Heavy Ions (energy per nucleon of 100 keV/amu or

higher) or multiple projectiles. You could compensate energy loss by coupling

bulk atoms with some thermostat or control heat transfer between electronic and

atomic subsystems with the two-temperature model ("fix_ttm"_fix_ttm.html).

At low velocities the electronic stopping is negligible. The electronic

friction is not applied to atoms whose kinetic energy is smaller than {Ecut},

or smaller than the lowest energy value given in the table in {file}.

Electronic stopping should be applied only when a projectile reaches bulk

material. This fix scans neighbor list and excludes atoms with fewer than

{minneigh} neighbors (by default one). If the pair potential cutoff is large,

minneigh should be increased, though not above the number of nearest neighbors

in bulk material. An alternative is to disable the check for neighbors by

setting {minneigh} to zero and using the {region} keyword. This is necessary

when running simulations of cluster bombardment.

If the {region} keyword is used, the atom must also be in the specified geometric

"region"_region.html in order to have electronic stopping applied to it. This is

useful if the position of the bulk material is fixed. By default the electronic

stopping is applied everywhere in the simulation cell.

:line

The energy ranges and stopping powers are read from the file {file}.

Lines starting with {#} and empty lines are ignored. Otherwise each

line must contain exactly [N+1] numbers, where [N] is the number of atom

types in the simulation.

The first column is the energy for which the stopping powers on that

line apply. The energies must be sorted from the smallest to the largest.

The other columns are the stopping powers \(S_e\) for each atom type,

in ascending order, in force "units"_units.html. The stopping powers for

intermediate energy values are calculated with linear interpolation between

2 nearest points.

For example:

# This is a comment

#       atom-1    atom-2

# eV    eV/Ang    eV/Ang  # units metal

 10        0        0

250       60       80

750      100      150 :pre

If an atom which would have electronic stopping applied to it has a

kinetic energy higher than the largest energy given in {file}, LAMMPS

will exit with an error message.

The stopping power depends on the energy of the ion and the target

material. The electronic stopping table can be obtained from

scientific publications, experimental databases or by using

"SRIM"_#SRIM software. Other programs such as "CasP"_#CasP or

"PASS"_#PASS can calculate the energy deposited as a function

of the impact parameter of the ion; these results can be used

to derive the stopping power.

[Restart, fix_modify, output, run start/stop, minimize info:]

No information about this fix is written to "binary restart

files"_restart.html.

The "fix_modify"_fix_modify.html options are not supported.

This fix computes a global scalar, which can be accessed by various

"output commands"_Howto_output.html. The scalar is the total energy

loss from electronic stopping applied by this fix since the start of

the latest run. It is considered "intensive".

The {start/stop} keywords of the "run"_run.html command have no effect

on this fix.

[Restrictions:]

This pair style is part of the USER-MISC package. It is only enabled if

LAMMPS was built with that package. See the "Build package"_Build_package.html

doc page for more info.

[Default:]

The default is no limitation by region, and minneigh = 1.

:line

:link(elstopping)

[(electronic stopping)] Wikipedia - Electronic Stopping Power: https://en.wikipedia.org/wiki/Stopping_power_%28particle_radiation%29

:link(Nordlund98)

[(Nordlund98)] Nordlund, Kai, et al.  Physical Review B 57.13 (1998): 7556.

:link(Nordlund95)

[(Nordlund95)] Nordlund, Kai. Computational materials science 3.4 (1995): 448-456.

:link(SRIM)

[(SRIM)] SRIM webpage: http://www.srim.org/

:link(CasP)

[(CasP)] CasP webpage: https://www.helmholtz-berlin.de/people/gregor-schiwietz/casp_en.html

:link(PASS)

[(PASS)] PASS webpage: https://www.sdu.dk/en/DPASS