2007-02-10 05:40:32 +08:00
|
|
|
"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
|
|
|
|
|
|
|
|
compute temp/ramp command :h3
|
|
|
|
|
|
|
|
[Syntax:]
|
|
|
|
|
|
|
|
compute ID group-ID temp/ramp vdim vlo vhi dim clo chi keyword value ... :pre
|
|
|
|
|
|
|
|
ID, group-ID are documented in "compute"_compute.html command
|
|
|
|
temp/ramp = style name of this compute command
|
|
|
|
vdim = {vx} or {vy} or {vz}
|
|
|
|
vlo,vhi = subtract velocities between vlo and vhi (velocity units)
|
|
|
|
dim = {x} or {y} or {z}
|
|
|
|
clo,chi = lower and upper bound of domain to subtract from (distance units)
|
2007-07-03 04:04:44 +08:00
|
|
|
zero or more keyword/value pairs may be appended
|
2007-02-10 05:40:32 +08:00
|
|
|
keyword = {units} :ul
|
|
|
|
{units} value = {lattice} or {box} :pre
|
|
|
|
|
|
|
|
[Examples:]
|
|
|
|
|
2009-04-30 00:54:14 +08:00
|
|
|
compute 2nd middle temp/ramp vx 0 8 y 2 12 units lattice :pre
|
2007-02-10 05:40:32 +08:00
|
|
|
|
|
|
|
[Description:]
|
|
|
|
|
|
|
|
Define a computation that calculates the temperature of a group of
|
2009-04-30 00:54:14 +08:00
|
|
|
atoms, after subtracting out an ramped velocity profile before
|
2007-02-10 05:40:32 +08:00
|
|
|
computing the kinetic energy. A compute of this style can be used by
|
|
|
|
any command that computes a temperature,
|
|
|
|
e.g. "thermo_modify"_thermo_modify.html, "fix
|
|
|
|
temp/rescale"_fix_temp_rescale.html, "fix npt"_fix_npt.html, etc.
|
|
|
|
|
2009-04-30 00:54:14 +08:00
|
|
|
The meaning of the arguments for this command which define the
|
|
|
|
velocity ramp are the same as for the "velocity ramp"_velocity.html
|
|
|
|
command which was presumably used to impose the velocity.
|
|
|
|
|
|
|
|
After the ramp velocity has been subtracted from the specified
|
|
|
|
dimension for each atom, the temperature is calculated by the formula
|
|
|
|
KE = dim/2 N k T, where KE = total kinetic energy of the group of
|
|
|
|
atoms (sum of 1/2 m v^2), dim = 2 or 3 = dimensionality of the
|
|
|
|
simulation, N = number of atoms in the group, k = Boltzmann constant,
|
|
|
|
and T = temperature.
|
2007-02-10 05:40:32 +08:00
|
|
|
|
|
|
|
The {units} keyword determines the meaning of the distance units used
|
|
|
|
for coordinates (c1,c2) and velocities (vlo,vhi). A {box} value
|
|
|
|
selects standard distance units as defined by the "units"_units.html
|
|
|
|
command, e.g. Angstroms for units = real or metal. A {lattice} value
|
|
|
|
means the distance units are in lattice spacings; e.g. velocity =
|
|
|
|
lattice spacings / tau. The "lattice"_lattice.html command must have
|
|
|
|
been previously used to define the lattice spacing.
|
|
|
|
|
2009-12-04 07:58:11 +08:00
|
|
|
A kinetic energy tensor, stored as a 6-element vector, is also
|
|
|
|
calculated by this compute for use in the computation of a pressure
|
|
|
|
tensor. The formula for the components of the tensor is the same as
|
|
|
|
the above formula, except that v^2 is replaced by vx*vy for the xy
|
|
|
|
component, etc. The 6 components of the vector are ordered xx, yy,
|
|
|
|
zz, xy, xz, yz.
|
2007-02-10 05:40:32 +08:00
|
|
|
|
|
|
|
The number of atoms contributing to the temperature is assumed to be
|
|
|
|
constant for the duration of the run; use the {dynamic} option of the
|
|
|
|
"compute_modify"_compute_modify.html command if this is not the case.
|
|
|
|
|
2008-03-12 00:37:01 +08:00
|
|
|
The removal of the ramped velocity component by this fix is
|
|
|
|
essentially computing the temperature after a "bias" has been removed
|
|
|
|
from the velocity of the atoms. If this compute is used with a fix
|
|
|
|
command that performs thermostatting then this bias will be subtracted
|
|
|
|
from each atom, thermostatting of the remaining thermal velocity will
|
|
|
|
be performed, and the bias will be added back in. Thermostatting
|
|
|
|
fixes that work in this way include "fix nvt"_fix_nvt.html, "fix
|
|
|
|
temp/rescale"_fix_temp_rescale.html, "fix
|
|
|
|
temp/berendsen"_fix_temp_berendsen, and "fix
|
|
|
|
langevin"_fix_langevin.html.
|
|
|
|
|
2007-02-10 05:40:32 +08:00
|
|
|
This compute subtracts out degrees-of-freedom due to fixes that
|
|
|
|
constrain molecular motion, such as "fix shake"_fix_shake.html and
|
|
|
|
"fix rigid"_fix_rigid.html. This means the temperature of groups of
|
|
|
|
atoms that include these constraints will be computed correctly. If
|
|
|
|
needed, the subtracted degrees-of-freedom can be altered using the
|
|
|
|
{extra} option of the "compute_modify"_compute_modify.html command.
|
|
|
|
|
2008-04-05 05:15:50 +08:00
|
|
|
See "this howto section"_Section_howto.html#4_16 of the manual for a
|
|
|
|
discussion of different ways to compute temperature and perform
|
|
|
|
thermostatting.
|
|
|
|
|
2008-01-03 03:25:15 +08:00
|
|
|
[Output info:]
|
|
|
|
|
2009-12-04 07:58:11 +08:00
|
|
|
This compute calculates a global scalar (the temperature) and a global
|
|
|
|
vector of length 6 (KE tensor), which can be accessed by indices 1-6.
|
|
|
|
These values can be used by any command that uses global scalar or
|
|
|
|
vector values from a compute as input. See "this
|
|
|
|
section"_Section_howto.html#4_15 for an overview of LAMMPS output
|
|
|
|
options.
|
|
|
|
|
2008-01-03 03:25:15 +08:00
|
|
|
The scalar value calculated by this compute is "intensive", meaning it
|
|
|
|
is independent of the number of atoms in the simulation. The vector
|
|
|
|
values are "extensive", meaning they scale with the number of atoms in
|
|
|
|
the simulation.
|
|
|
|
|
2010-01-24 07:20:05 +08:00
|
|
|
The scalar value will be in temperature "units"_units.html. The
|
|
|
|
vector values will be in energy "units"_units.html.
|
|
|
|
|
2007-02-10 05:40:32 +08:00
|
|
|
[Restrictions:] none
|
|
|
|
|
|
|
|
[Related commands:]
|
|
|
|
|
|
|
|
"compute temp"_compute_temp.html, "compute
|
2009-04-30 00:54:14 +08:00
|
|
|
temp/profie"_compute_temp_profile.html, "compute
|
2007-06-20 20:56:17 +08:00
|
|
|
temp/deform"_compute_temp_deform.html, "compute
|
2007-02-10 05:40:32 +08:00
|
|
|
pressure"_compute_pressure.html
|
|
|
|
|
|
|
|
[Default:]
|
|
|
|
|
|
|
|
The option default is units = lattice.
|