forked from lijiext/lammps
71 lines
2.2 KiB
Plaintext
71 lines
2.2 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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dynamical_matrix command :h3
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[Syntax:]
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dynamical_matrix group-ID style gamma args keyword value ... :pre
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group-ID = ID of group of atoms to displace :ulb,l
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style = {regular} or {eskm} :l
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gamma = finite different displacement length (distance units) :l
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one or more keyword/arg pairs may be appended :l
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keyword = {file} or {binary}
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{file} name = name of output file for the dynamical matrix
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{binary} arg = {yes} or {no} or {gzip} :pre
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:ule
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[Examples:]
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dynamical_matrix 1 regular 0.000001
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dynamical_matrix 1 eskm 0.000001
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dynamical_matrix 3 regular 0.00004 file dynmat.dat
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dynamical_matrix 5 eskm 0.00000001 file dynamical.dat binary yes :pre
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[Description:]
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Calculate the dynamical matrix by finite difference of the selected group,
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:c,image(JPG/dynamical_matrix_dynmat.jpg)
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where D is the dynamical matrix and Phi is the force constant matrix defined by
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:c,image(JPG/dynamical_matrix_force_constant.jpg).
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The output for the dynamical matrix is printed three elements at a time. The
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three elements are the three beta elements for a respective i/alpha/j combination.
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Each line is printed in order of j increasing first, alpha second, and i last.
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If the style eskm is selected, the dynamical matrix will be in units of inverse squared
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femtoseconds. These units will then conveniently leave frequencies in THz, where
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frequencies, represented as omega, can be calculated from
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:c, image(Eqs/dynamical_matrix_phonons.jpg)
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[Restrictions:]
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The command collects an array of nine times the number of atoms in a group
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on every single MPI rank, so the memory requirements can be very significant
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for large systems.
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This command is part of the USER-PHONON package. It is only enabled if
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LAMMPS was built with that package. See the "Build
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package"_Build_package.html doc page for more info.
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[Related commands:]
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"fix phonon"_fix_phonon.html
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"compute hma"_compute_hma.html uses an analytic formulation of the hessian
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provided by Pair's single_hessian.
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[Default:]
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The default settings are file = "dynmat.dyn", binary = no
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