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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2007-06-28 23:07:55 +08:00
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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 used in Ei are an average over the 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 this formulation.
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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.
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2006-09-22 00:22:34 +08:00
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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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2007-06-26 08:03:39 +08:00
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For this style, coefficients for the Ei formula can be specified in
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eiher the input script or data file. 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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2007-06-26 08:03:39 +08:00
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Coefficients for the Eaa formula can only be specified in the data
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file. 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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2007-06-26 08:03:39 +08:00
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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#2_3
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section for more info on packages.
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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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