2006-09-22 00:22:34 +08:00
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"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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[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 :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 chi
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used in Ei is an average over 3 possible chi orientations. The
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subscripts on the various theta's refer to different combinations of
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atoms i,j,k,l used to form the angle; theta1, theta2, theta3 are the
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equilibrium positions of those angles.
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2006-09-28 03:12:31 +08:00
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See "(Sun)"_#Sun for a description of the COMPASS class2 force field.
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2006-09-22 00:22:34 +08:00
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The following coefficients must be defined for each improper type via the
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"improper_coeff"_improper_coeff.html command as in the example above, or in
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the data file or restart files read by the "read_data"_read_data.html
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or "read_restart"_read_restart.html commands:
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2007-06-25 23:17:40 +08:00
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For this style, only coefficients for the Ei formula can be specified
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in the input script. These are the 2 coefficients:
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2006-09-22 00:22:34 +08:00
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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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2007-06-25 23:17:40 +08:00
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Coefficients for the Eaa formula must be specified in the data file.
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For the Eaa formula, the coefficients are listed under a
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2006-09-22 00:22:34 +08:00
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"AngleAngle Coeffs" heading and each line lists 6 coefficients:
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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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[Restrictions:]
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2007-06-25 23:17:40 +08:00
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This improper style is part of the "class2" package. It is only
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enabled if LAMMPS was built with that package. See the "Making
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LAMMPS"_Section_start.html#2_2 section for more info.
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2006-09-22 00:22:34 +08:00
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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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2006-09-28 03:12:31 +08:00
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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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