forked from lijiext/lammps
96 lines
3.6 KiB
Plaintext
96 lines
3.6 KiB
Plaintext
"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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compute temp/eff command :h3
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[Syntax:]
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compute ID group-ID temp/eff :pre
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ID, group-ID are documented in "compute"_compute.html command
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temp/eff = style name of this compute command :ul
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[Examples:]
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compute 1 all temp/eff
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compute myTemp mobile temp/eff :pre
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[Description:]
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Define a computation that calculates the temperature of a group of
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nuclei and electrons in the "electron force field"_pair_eff.html
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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. "thermo_modify"_thermo_modify.html, "fix
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npt/eff"_fix_npt_eff.html, etc.
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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 "pair_eff"_pair_style.html
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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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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 "thermo"_thermo.html command, the user should apply a
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"thermo_modify"_thermo_modify.html command, as shown in the following
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example:
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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 :pre
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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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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 {dynamic} option of the
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"compute_modify"_compute_modify.html command if this is not the case.
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This compute subtracts out degrees-of-freedom due to fixes that
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constrain molecular motion, such as "fix shake"_fix_shake.html and
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"fix rigid"_fix_rigid.html. 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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{extra} option of the "compute_modify"_compute_modify.html command.
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See "this howto section"_Section_howto.html#4_16 of the manual for a
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discussion of different ways to compute temperature and perform
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thermostatting.
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[Output info:]
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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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[Restrictions:]
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This compute is part of the "user-eff" package. It is only enabled if
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LAMMPS was built with that package. See the "Making
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LAMMPS"_Section_start.html#2_3 section for more info.
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[Related commands:]
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"compute temp/partial"_compute_temp_partial.html, "compute
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temp/region"_compute_temp_region.html, "compute
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pressure"_compute_pressure.html
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[Default:] none
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