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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@10079 f3b2605a-c512-4ea7-a41b-209d697bcdaa

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sjplimp 2013-06-17 15:20:05 +00:00
parent 61a1847026
commit fbdc189121
2 changed files with 34 additions and 18 deletions
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26
doc/fix_efield.html
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@ -28,14 +28,20 @@ fix kick external-field efield 0.0 0.0 v_oscillate
<P><B>Description:</B>
</P>
<P>Add a force F = qE to each charged atom in the group due to an
external electric field being applied to the system.
external electric field being applied to the system. If the system
contains point-dipoles, also add a torque on the dipoles due to the
external electric field.
</P>
<P>Any of the 3 quantities defining the E-field components can be
specified as an equal-style or atom-style <A HREF = "variable.html">variable</A>,
namely <I>ex</I>, <I>ey</I>, <I>ez</I>. If the value is a variable, it should be
specified as v_name, where name is the variable name. In this case,
the variable will be evaluated each timestep, and its value used to
determine the E-field component.
<P>For charges, any of the 3 quantities defining the E-field components
can be specified as an equal-style or atom-style
<A HREF = "variable.html">variable</A>, namely <I>ex</I>, <I>ey</I>, <I>ez</I>. If the value is a
variable, it should be specified as v_name, where name is the variable
name. In this case, the variable will be evaluated each timestep, and
its value used to determine the E-field component. For point-dipoles,
equal-style variables can be used, but atom-style variables are not
currently supported, since they imply a spatial gradient in the
electric field which means additional terms with gradients of the
field are required for the force and torque on dipoles.
</P>
<P>Equal-style variables can specify formulas with various mathematical
functions, and include <A HREF = "thermo_style.html">thermo_style</A> command
@ -59,14 +65,16 @@ output</A>. This is a fictitious quantity but is
needed so that the <A HREF = "minimize.html">minimize</A> command can include the
forces added by this fix in a consistent manner. I.e. there is a
decrease in potential energy when atoms move in the direction of the
added force.
added force. The potential energy contribution of dipoles in the
electric field is also included.
</P>
<P>This fix computes a global scalar and a global 3-vector of forces,
which can be accessed by various <A HREF = "Section_howto.html#howto_15">output
commands</A>. The scalar is the potential
energy discussed above. The vector is the total force added to the
group of atoms. The scalar and vector values calculated by this fix
are "extensive".
are "extensive". The added torques for point-dipoles cannot currently
be output in this manner.
</P>
<P>No parameter of this fix can be used with the <I>start/stop</I> keywords of
the <A HREF = "run.html">run</A> command.

26
doc/fix_efield.txt
View File

@ -25,14 +25,20 @@ fix kick external-field efield 0.0 0.0 v_oscillate :pre
[Description:]
Add a force F = qE to each charged atom in the group due to an
external electric field being applied to the system.
external electric field being applied to the system. If the system
contains point-dipoles, also add a torque on the dipoles due to the
external electric field.
Any of the 3 quantities defining the E-field components can be
specified as an equal-style or atom-style "variable"_variable.html,
namely {ex}, {ey}, {ez}. If the value is a variable, it should be
specified as v_name, where name is the variable name. In this case,
the variable will be evaluated each timestep, and its value used to
determine the E-field component.
For charges, any of the 3 quantities defining the E-field components
can be specified as an equal-style or atom-style
"variable"_variable.html, namely {ex}, {ey}, {ez}. If the value is a
variable, it should be specified as v_name, where name is the variable
name. In this case, the variable will be evaluated each timestep, and
its value used to determine the E-field component. For point-dipoles,
equal-style variables can be used, but atom-style variables are not
currently supported, since they imply a spatial gradient in the
electric field which means additional terms with gradients of the
field are required for the force and torque on dipoles.
Equal-style variables can specify formulas with various mathematical
functions, and include "thermo_style"_thermo_style.html command
@ -56,14 +62,16 @@ output"_thermo_style.html. This is a fictitious quantity but is
needed so that the "minimize"_minimize.html command can include the
forces added by this fix in a consistent manner. I.e. there is a
decrease in potential energy when atoms move in the direction of the
added force.
added force. The potential energy contribution of dipoles in the
electric field is also included.
This fix computes a global scalar and a global 3-vector of forces,
which can be accessed by various "output
commands"_Section_howto.html#howto_15. The scalar is the potential
energy discussed above. The vector is the total force added to the
group of atoms. The scalar and vector values calculated by this fix
are "extensive".
are "extensive". The added torques for point-dipoles cannot currently
be output in this manner.
No parameter of this fix can be used with the {start/stop} keywords of
the "run"_run.html command.