forked from lijiext/lammps
166 lines
6.7 KiB
Plaintext
166 lines
6.7 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Commands_all.html)
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:line
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fix electron/stopping command :h3
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[Syntax:]
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fix ID group-ID electron/stopping Ecut file keyword value ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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electron/stopping = style name of this fix command :l
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Ecut = minimum kinetic energy for electronic stopping (energy units) :l
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file = name of the file containing the electronic stopping power table :l
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zero or more keyword/value pairs may be appended to args :l
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keyword = {region} or {minneigh} :l
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{region} value = region-ID
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region-ID = region, whose atoms will be affected by this fix
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{minneigh} value = minneigh
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minneigh = minimum number of neighbors an atom to have stopping applied :pre
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:ule
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[Examples:]
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fix el all electron/stopping 10.0 elstop-table.txt
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fix el all electron/stopping 10.0 elstop-table.txt minneigh 3
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fix el mygroup electron/stopping 1.0 elstop-table.txt region bulk :pre
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[Description:]
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This fix implements inelastic energy loss for fast projectiles in solids. It
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applies a friction force to fast moving atoms to slow them down due to
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"electronic stopping"_#elstopping (energy lost via electronic collisions per
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unit of distance). This fix should be used for simulation of irradiation
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damage or ion implantation, where the ions can lose noticeable amounts of
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energy from electron excitations. If the electronic stopping power is not
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considered, the simulated range of the ions can be severely overestimated
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("Nordlund98"_#Nordlund98, "Nordlund95"_#Nordlund95).
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The electronic stopping is implemented by applying a friction force
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to each atom as:
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\begin\{equation\}
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\vec\{F\}_i = \vec\{F\}^0_i - \frac\{\vec\{v\}_i\}\{\|\vec\{v\}_i\|\} \cdot S_e
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\end\{equation\}
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where \(\vec\{F\}_i\) is the resulting total force on the atom.
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\(\vec\{F\}^0_i\) is the original force applied to the atom, \(\vec\{v\}_i\) is
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its velocity and \(S_e\) is the stopping power of the ion.
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NOTE: In addition to electronic stopping, atomic cascades and irradiation
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simulations require the use of an adaptive timestep (see
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"fix dt/reset"_fix_dt_reset.html) and the repulsive ZBL potential (see
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"ZBL"_pair_zbl.html potential) or similar. Without these settings the
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interaction between the ion and the target atoms will be faulty. It is also
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common to use in such simulations a thermostat ("fix_nvt"_fix_nh.html) in
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the borders of the simulation cell.
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NOTE: This fix removes energy from fast projectiles without depositing it as a
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heat to the simulation cell. Such implementation might lead to the unphysical
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results when the amount of energy deposited to the electronic system is large,
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e.g. simulations of Swift Heavy Ions (energy per nucleon of 100 keV/amu or
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higher) or multiple projectiles. You could compensate energy loss by coupling
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bulk atoms with some thermostat or control heat transfer between electronic and
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atomic subsystems with the two-temperature model ("fix_ttm"_fix_ttm.html).
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At low velocities the electronic stopping is negligible. The electronic
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friction is not applied to atoms whose kinetic energy is smaller than {Ecut},
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or smaller than the lowest energy value given in the table in {file}.
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Electronic stopping should be applied only when a projectile reaches bulk
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material. This fix scans neighbor list and excludes atoms with fewer than
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{minneigh} neighbors (by default one). If the pair potential cutoff is large,
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minneigh should be increased, though not above the number of nearest neighbors
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in bulk material. An alternative is to disable the check for neighbors by
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setting {minneigh} to zero and using the {region} keyword. This is necessary
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when running simulations of cluster bombardment.
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If the {region} keyword is used, the atom must also be in the specified
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geometric "region"_region.html in order to have electronic stopping applied to
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it. This is useful if the position of the bulk material is fixed. By default
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the electronic stopping is applied everywhere in the simulation cell.
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:line
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The energy ranges and stopping powers are read from the file {file}.
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Lines starting with {#} and empty lines are ignored. Otherwise each
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line must contain exactly [N+1] numbers, where [N] is the number of atom
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types in the simulation.
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The first column is the energy for which the stopping powers on that
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line apply. The energies must be sorted from the smallest to the largest.
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The other columns are the stopping powers \(S_e\) for each atom type,
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in ascending order, in force "units"_units.html. The stopping powers for
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intermediate energy values are calculated with linear interpolation between
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2 nearest points.
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For example:
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# This is a comment
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# atom-1 atom-2
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# eV eV/Ang eV/Ang # units metal
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10 0 0
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250 60 80
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750 100 150 :pre
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If an atom which would have electronic stopping applied to it has a
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kinetic energy higher than the largest energy given in {file}, LAMMPS
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will exit with an error message.
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The stopping power depends on the energy of the ion and the target
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material. The electronic stopping table can be obtained from
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scientific publications, experimental databases or by using
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"SRIM"_#SRIM software. Other programs such as "CasP"_#CasP or
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"PASS"_#PASS can calculate the energy deposited as a function
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of the impact parameter of the ion; these results can be used
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to derive the stopping power.
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[Restart, fix_modify, output, run start/stop, minimize info:]
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No information about this fix is written to "binary restart
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files"_restart.html.
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The "fix_modify"_fix_modify.html options are not supported.
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This fix computes a global scalar, which can be accessed by various
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"output commands"_Howto_output.html. The scalar is the total energy
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loss from electronic stopping applied by this fix since the start of
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the latest run. It is considered "intensive".
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The {start/stop} keywords of the "run"_run.html command have no effect
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on this fix.
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[Restrictions:]
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This pair style is part of the USER-MISC package. It is only enabled if
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LAMMPS was built with that package. See the "Build package"_Build_package.html
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doc page for more info.
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[Default:]
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The default is no limitation by region, and minneigh = 1.
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:line
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:link(elstopping)
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[(electronic stopping)] Wikipedia - Electronic Stopping Power: https://en.wikipedia.org/wiki/Stopping_power_%28particle_radiation%29
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:link(Nordlund98)
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[(Nordlund98)] Nordlund, Kai, et al. Physical Review B 57.13 (1998): 7556.
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:link(Nordlund95)
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[(Nordlund95)] Nordlund, Kai. Computational materials science 3.4 (1995): 448-456.
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:link(SRIM)
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[(SRIM)] SRIM webpage: http://www.srim.org/
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:link(CasP)
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[(CasP)] CasP webpage: https://www.helmholtz-berlin.de/people/gregor-schiwietz/casp_en.html
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:link(PASS)
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[(PASS)] PASS webpage: https://www.sdu.dk/en/DPASS
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