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lammps/doc/improper_class2.txt
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improper_class2.txt
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"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)
:line
improper_style class2 command :h3
[Syntax:]
improper_style class2 :pre
[Examples:]
improper_style class2
improper_coeff 1 100.0 0 :pre
[Description:]
The {class2} improper style uses the potential
:c,image(Eqs/improper_class2.jpg)
where Ei is the improper term and Eaa is an angle-angle term. The chi
used in Ei is an average over 3 possible chi orientations. The
subscripts on the various theta's refer to different combinations of
atoms i,j,k,l used to form the angle; theta1, theta2, theta3 are the
equilibrium positions of those angles.
See "(Sun)"_#Sun for a description of the COMPASS class2 force field.
The following coefficients must be defined for each improper type via the
"improper_coeff"_improper_coeff.html command as in the example above, or in
the data file or restart files read by the "read_data"_read_data.html
or "read_restart"_read_restart.html commands:
For this style, only coefficients for the Ei formula can be specified
in the input script. These are the 2 coefficients:
K (energy/radian^2)
X0 (degrees) :ul
X0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of K are in energy/radian^2.
Coefficients for the Eaa formula must be specified in the data file.
For the Eaa formula, the coefficients are listed under a
"AngleAngle Coeffs" heading and each line lists 6 coefficients:
M1 (energy/distance)
M2 (energy/distance)
M3 (energy/distance)
theta1 (degrees)
theta2 (degrees)
theta3 (degrees) :ul
The theta values are specified in degrees, but LAMMPS converts them to
radians internally; hence the units of M are in energy/radian^2.
[Restrictions:]
This improper style is part of the "class2" package. It is only
enabled if LAMMPS was built with that package. See the "Making
LAMMPS"_Section_start.html#2_2 section for more info.
[Related commands:]
"improper_coeff"_improper_coeff.html
[Default:] none
:line
:link(Sun)
[(Sun)] Sun, J Phys Chem B 102, 7338-7364 (1998).
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