2010-09-02 03:53:20 +08:00
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<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>
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<HR>
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<H3>compute temp/eff command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>compute ID group-ID temp/eff
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
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<LI>temp/eff = style name of this compute command
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>compute 1 all temp/eff
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compute myTemp mobile temp/eff
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Define a computation that calculates the temperature of a group of
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2010-09-02 04:48:58 +08:00
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nuclei and electrons in the <A HREF = "pair_eff.html">electron force field</A>
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model. A compute of this style can be used by commands that compute a
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temperature, e.g. <A HREF = "thermo_modify.html">thermo_modify</A>, <A HREF = "fix_npt_eff.html">fix
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2010-09-02 03:53:20 +08:00
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npt/eff</A>, etc.
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</P>
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<P>The temperature is calculated by the formula KE = dim/2 N k T, where
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KE = total kinetic energy of the group of atoms (sum of 1/2 m v^2 for
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nuclei and sum of 1/2 (m v^2 + 3/4 m s^2) for electrons, where s
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includes the radial electron velocity contributions), dim = 2 or 3 =
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dimensionality of the simulation, N = number of atoms (only total
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number of nuclei in the eFF (see the <A HREF = "pair_style.html">pair_eff</A>
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command) in the group, k = Boltzmann constant, and T = temperature.
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This expression is summed over all nuclear and electronic degrees of
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freedom, essentially by setting the kinetic contribution to the heat
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capacity to 3/2k (where only nuclei contribute). This subtlety is
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valid for temperatures well below the Fermi temperature, which for
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densities two to five times the density of liquid H2 ranges from
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86,000 to 170,000 K.
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</P>
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<P>IMPORTANT NOTE: For eFF models, in order to override the default
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temperature reported by LAMMPS in the thermodynamic quantities
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reported via the <A HREF = "thermo.html">thermo</A> command, the user should apply a
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<A HREF = "thermo_modify.html">thermo_modify</A> command, as shown in the following
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example:
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</P>
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<PRE>compute effTemp all temp/eff
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thermo_style custom step etotal pe ke temp press
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thermo_modify temp effTemp
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</PRE>
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<P>A 6-component kinetic energy tensor is also calculated by this compute
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for use in the computation of a pressure tensor. The formula for the
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components of the tensor is the same as the above formula, except that
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v^2 is replaced by vx * vy for the xy component, etc. For the eFF,
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again, the radial electronic velocities are also considered.
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</P>
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<P>The number of atoms contributing to the temperature is assumed to be
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constant for the duration of the run; use the <I>dynamic</I> option of the
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<A HREF = "compute_modify.html">compute_modify</A> command if this is not the case.
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</P>
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<P>This compute subtracts out degrees-of-freedom due to fixes that
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constrain molecular motion, such as <A HREF = "fix_shake.html">fix shake</A> and
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<A HREF = "fix_rigid.html">fix rigid</A>. This means the temperature of groups of
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atoms that include these constraints will be computed correctly. If
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needed, the subtracted degrees-of-freedom can be altered using the
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<I>extra</I> option of the <A HREF = "compute_modify.html">compute_modify</A> command.
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</P>
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2011-08-26 01:01:01 +08:00
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<P>See <A HREF = "Section_howto.html#howto_16">this howto section</A> of the manual for
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a discussion of different ways to compute temperature and perform
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2010-09-02 03:53:20 +08:00
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thermostatting.
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</P>
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<P><B>Output info:</B>
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</P>
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<P>The scalar value calculated by this compute is "intensive", meaning it
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is independent of the number of atoms in the simulation. The vector
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values are "extensive", meaning they scale with the number of atoms in
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the simulation.
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</P>
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<P><B>Restrictions:</B>
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</P>
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2011-08-27 02:53:00 +08:00
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<P>This compute is part of the USER-EFF package. It is only enabled if
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2011-08-26 00:46:23 +08:00
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LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making
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2010-09-02 03:53:20 +08:00
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LAMMPS</A> section for more info.
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "compute_temp_partial.html">compute temp/partial</A>, <A HREF = "compute_temp_region.html">compute
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temp/region</A>, <A HREF = "compute_pressure.html">compute
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pressure</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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