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rLAMMPS lammps
compute_ke_eff.html
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<HTML>
<CENTER><A
HREF =
"http://lammps.sandia.gov"
>
LAMMPS WWW Site
</A>
-
<A
HREF =
"Manual.html"
>
LAMMPS Documentation
</A>
-
<A
HREF =
"Section_commands.html#comm"
>
LAMMPS Commands
</A>
</CENTER>
<HR>
<H3>
compute ke/eff command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
compute ID group-ID ke/eff
</PRE>
<UL><LI>
ID, group-ID are documented in
<A
HREF =
"compute.html"
>
compute
</A>
command
<LI>
ke/eff = style name of this compute command
</UL>
<P><B>
Examples:
</B>
</P>
<PRE>
compute 1 all ke/eff
</PRE>
<P><B>
Description:
</B>
</P>
<P>
Define a computation that calculates the kinetic energy of motion of a
group of eFF particles (nuclei and electrons), as modeled with the
<A
HREF =
"pair_eff.html"
>
electronic force field
</A>
.
</P>
<P>
The kinetic energy for each nucleus is computed as 1/2 m v^2 and the
kinetic energy for each electron is computed as 1/2(me v^2 + 3/4 me
s^2), where m corresponds to the nuclear mass, me to the electron
mass, v to the translational velocity of each particle, and s to the
radial velocity of the electron, respectively.
</P>
<P>
There is a subtle difference between the quantity calculated by this
compute and the kinetic energy calculated by the
<I>
ke
</I>
or
<I>
etotal
</I>
keyword used in thermodynamic output, as specified by the
<A
HREF =
"thermo_style.html"
>
thermo_style
</A>
command. For this compute, kinetic
energy is "translational" and "radial" (only for electrons) kinetic
energy, calculated by the simple formula above. For thermodynamic
output, the
<I>
ke
</I>
keyword infers kinetic energy from the temperature of
the system with 1/2 Kb T of energy for each degree of freedom. For
the eFF temperature computation via the
<A
HREF =
"compute_temp_eff.html"
>
compute
temp_eff
</A>
command, these are the same. But
different computes that calculate temperature can subtract out
different non-thermal components of velocity and/or include other
degrees of freedom.
</P>
<P>
IMPRORTANT NOTE: The temperature in eFF models should be monitored via
the
<A
HREF =
"compute_temp_eff.html"
>
compute temp/eff
</A>
command, which can be
printed with thermodynamic output by using the
<A
HREF =
"thermo_modify.html"
>
thermo_modify
</A>
command, as shown in the following
example:
</P>
<PRE>
compute effTemp all temp/eff
thermo_style custom step etotal pe ke temp press
thermo_modify temp effTemp
</PRE>
<P>
See
<A
HREF =
"compute_temp_eff.html"
>
compute temp/eff
</A>
.
</P>
<P><B>
Output info:
</B>
</P>
<P>
This compute calculates a global scalar (the KE). This value can be
used by any command that uses a global scalar value from a compute as
input. See
<A
HREF =
"Section_howto.html#howto_15"
>
this section
</A>
for an overview
of LAMMPS output options.
</P>
<P>
The scalar value calculated by this compute is "extensive". The
scalar value will be in energy
<A
HREF =
"units.html"
>
units
</A>
.
</P>
<P><B>
Restrictions:
</B>
</P>
<P>
This compute is part of the USER-EFF package. It is only enabled if
LAMMPS was built with that package. See the
<A
HREF =
"Section_start.html#start_3"
>
Making
LAMMPS
</A>
section for more info.
</P>
<P><B>
Related commands:
</B>
none
</P>
<P><B>
Default:
</B>
none
</P>
</HTML>
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