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added tfac_insert keyword 

git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@14109 f3b2605a-c512-4ea7-a41b-209d697bcdaa
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athomps 2015-10-13 15:53:41 +00:00
parent 97878b1a9f
commit 39e8123a02
1 changed files with 19 additions and 3 deletions
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22
doc/fix_gcmc.txt
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@ -23,7 +23,7 @@ T = temperature of the ideal gas reservoir (temperature units) :l
mu = chemical potential of the ideal gas reservoir (energy units) :l
translate = maximum Monte Carlo translation distance (length units) :l
zero or more keyword/value pairs may be appended to args :l
keyword = {mol}, {region}, {maxangle}, {pressure}, {fugacity_coeff}, {full_energy}, {charge}, {group}, {grouptype}, or {intra_energy}
keyword = {mol}, {region}, {maxangle}, {pressure}, {fugacity_coeff}, {full_energy}, {charge}, {group}, {grouptype}, {intra_energy}, or {tfac_insert}
{mol} value = template-ID
template-ID = ID of molecule template specified in a separate "molecule"_molecule.html command
{shake} value = fix-ID
@ -40,7 +40,8 @@ keyword = {mol}, {region}, {maxangle}, {pressure}, {fugacity_coeff}, {full_energ
{grouptype} values = type group-ID
type = atom type (int)
group-ID = group-ID for inserted atoms (string)
{intra_energy} value = intramolecular energy (energy units) :pre
{intra_energy} value = intramolecular energy (energy units)
{tfac_insert} value = scale up/down temperature of inserted atoms (unitless) :pre
:ule
[Examples:]
@ -131,7 +132,9 @@ distance. See the "neighbor"_neighbor.html command for details.
When an atom or molecule is to be inserted, its
coordinates are chosen at a random position within the current
simulation cell or region, and new atom velocities are randomly chosen from
the specified temperature distribution given by T. Relative
the specified temperature distribution given by T. The effective
temperature for new atom velocities can be increased or decreased
using the optional keyword {tfac_insert} (see below). Relative
coordinates for atoms in a molecule are taken from the template
molecule provided by the user. The center of mass of the molecule
is placed at the insertion point. The orientation of the molecule
@ -217,6 +220,19 @@ deleted. For molecules that have a non-zero intramolecular energy, this
will ensure roughly the same behavior whether or not the {full_energy}
option is used.
Inserted atoms and molecules are assigned random velocities based on the
specified temperature T. Because the relative velocity of
all atoms in the molecule is zero, this may result in inserted molecules
that are systematically too cold. In addition, the intramolecular potential
energy of the inserted molecule may casue the kinetic energy
of the molecule to quickly increase or decrease after insertion.
The {tfac_insert} keyword allows the user to counteract these effects
by changing the temperature used to assign velocities to
inserted atoms and molecules by a constant factor. For a
particular application, some experimentation may be required
to find a value of {tfac_insert} that results in inserted molecules that
equilibrate quickly to the correct temperature.
Some fixes have an associated potential energy. Examples of such fixes
include: "efield"_fix_efield.html, "gravity"_fix_gravity.html,
"addforce"_fix_addforce.html, "langevin"_fix_langevin.html,