forked from lijiext/lammps
125 lines
4.2 KiB
Plaintext
125 lines
4.2 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,Section_commands.html#comm)
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:line
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improper_style class2 command :h3
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improper_style class2/omp command :h3
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[Syntax:]
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improper_style class2 :pre
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[Examples:]
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improper_style class2
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improper_coeff 1 100.0 0
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improper_coeff * aa 0.0 0.0 0.0 115.06 130.01 115.06 :pre
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[Description:]
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The {class2} improper style uses the potential
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:c,image(Eqs/improper_class2.jpg)
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where Ei is the improper term and Eaa is an angle-angle term. The 3 X
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terms in Ei are an average over 3 out-of-plane angles.
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The 4 atoms in an improper quadruplet (listed in the data file read by
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the "read_data"_read_data.html command) are ordered I,J,K,L. X_IJKL
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refers to the angle between the plane of I,J,K and the plane of J,K,L,
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and the bond JK lies in both planes. Similarly for X_KJLI and X_LJIK.
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Note that atom J appears in the common bonds (JI, JK, JL) of all 3 X
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terms. Thus J (the 2nd atom in the quadruplet) is the atom of
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symmetry in the 3 X angles.
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The subscripts on the various theta's refer to different combinations
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of 3 atoms (I,J,K,L) used to form a particular angle. E.g. Theta_IJL
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is the angle formed by atoms I,J,L with J in the middle. Theta1,
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theta2, theta3 are the equilibrium positions of those angles. Again,
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atom J (the 2nd atom in the quadruplet) is the atom of symmetry in the
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theta angles, since it is always the center atom.
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Since atom J is the atom of symmetry, normally the bonds J-I, J-K, J-L
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would exist for an improper to be defined between the 4 atoms, but
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this is not required.
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See "(Sun)"_#Sun for a description of the COMPASS class2 force field.
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Coefficients for the Ei and Eaa formulas must be defined for each
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improper type via the "improper_coeff"_improper_coeff.html command as
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in the example above, or in the data file or restart files read by the
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"read_data"_read_data.html or "read_restart"_read_restart.html
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commands.
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These are the 2 coefficients for the Ei formula:
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K (energy/radian^2)
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X0 (degrees) :ul
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X0 is specified in degrees, but LAMMPS converts it to radians
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internally; hence the units of K are in energy/radian^2.
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For the Eaa formula, each line in a
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"improper_coeff"_improper_coeff.html command in the input script lists
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7 coefficients, the first of which is "aa" to indicate they are
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AngleAngle coefficients. In a data file, these coefficients should be
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listed under a "AngleAngle Coeffs" heading and you must leave out the
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"aa", i.e. only list 6 coefficients after the improper type.
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aa
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M1 (energy/distance)
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M2 (energy/distance)
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M3 (energy/distance)
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theta1 (degrees)
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theta2 (degrees)
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theta3 (degrees) :ul
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The theta values are specified in degrees, but LAMMPS converts them to
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radians internally; hence the units of M are in energy/radian^2.
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:line
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Styles with a {cuda}, {gpu}, {intel}, {kk}, {omp}, or {opt} suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in "Section_accelerate"_Section_accelerate.html
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if LAMMPS was built with those packages. See the "Making
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LAMMPS"_Section_start.html#start_3 section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the "-suffix command-line
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switch"_Section_start.html#start_7 when you invoke LAMMPS, or you can
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use the "suffix"_suffix.html command in your input script.
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See "Section_accelerate"_Section_accelerate.html of the manual for
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more instructions on how to use the accelerated styles effectively.
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:line
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[Restrictions:]
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This improper style can only be used if LAMMPS was built with the
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CLASS2 package. See the "Making LAMMPS"_Section_start.html#start_3
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section for more info on packages.
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[Related commands:]
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"improper_coeff"_improper_coeff.html
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[Default:] none
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:line
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:link(Sun)
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[(Sun)] Sun, J Phys Chem B 102, 7338-7364 (1998).
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