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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@1753 f3b2605a-c512-4ea7-a41b-209d697bcdaa

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sjplimp 2008-04-16 22:15:33 +00:00
parent e9a2d5abb3
commit e0aab9e65e
2 changed files with 32 additions and 24 deletions
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28
doc/fix_langevin.html
View File

@ -46,26 +46,30 @@ interaction with a background implicit solvent. Used with <A HREF = "fix_nve.ht
nve</A>, this command performs Brownian dynamics (BD), since
the total force on each atom will have the form:
</P>
<PRE>F = Fc + Ff + Fr
<PRE>F = Fc + Ff + Fr
Ff = - (m / damp) v
Fr is proportional to sqrt(Kb T m / (dt damp))
</PRE>
<P>Fc is the conservative force computed via the usual inter-particle
interactions (<A HREF = "pair_style.html">pair_style</A>,
<A HREF = "bond_style.html">bond_style</A>, etc).
</P>
<P>The Ff and Fr terms are added by this fix. Ff = - gamma v and is a
frictional drag or viscous damping term proportional to the particle's
velocity. Gamma for each atom is computed as m/damp, where m is the
mass of the particle and damp is the damping factor specified by the
user.
<P>The Ff and Fr terms are added by this fix.
</P>
<P>Ff is a frictional drag or viscous damping term proportional to the
particle's velocity. The proportionality constant for each atom is
computed as m/damp, where m is the mass of the particle and damp is
the damping factor specified by the user.
</P>
<P>Fr is a force due to solvent atoms at a temperature T randomly bumping
into the particle. As derived from the fluctuation/dissipation
theorem, its magnitude is proportional to sqrt(T m / dt damp), where T
is the desired temperature, m is the mass of the particle, dt is the
timestep size, and damp is the damping factor. Random numbers are
used to randomize the direction and magnitude of this force as
described in <A HREF = "#Dunweg">(Dunweg)</A>, where a uniform random number is used
(instead of a Gaussian random number) for speed.
theorem, its magnitude as shown above is proportional to sqrt(Kb T m /
dt damp), where Kb is the Boltzmann constant, T is the desired
temperature, m is the mass of the particle, dt is the timestep size,
and damp is the damping factor. Random numbers are used to randomize
the direction and magnitude of this force as described in
<A HREF = "#Dunweg">(Dunweg)</A>, where a uniform random number is used (instead of
a Gaussian random number) for speed.
</P>
<P>Note that the thermostat effect of this fix is applied to only the
translational degrees of freedom for the particles, which is an

28
doc/fix_langevin.txt
View File

@ -37,26 +37,30 @@ interaction with a background implicit solvent. Used with "fix
nve"_fix_nve.html, this command performs Brownian dynamics (BD), since
the total force on each atom will have the form:
F = Fc + Ff + Fr :pre
F = Fc + Ff + Fr
Ff = - (m / damp) v
Fr is proportional to sqrt(Kb T m / (dt damp)) :pre
Fc is the conservative force computed via the usual inter-particle
interactions ("pair_style"_pair_style.html,
"bond_style"_bond_style.html, etc).
The Ff and Fr terms are added by this fix. Ff = - gamma v and is a
frictional drag or viscous damping term proportional to the particle's
velocity. Gamma for each atom is computed as m/damp, where m is the
mass of the particle and damp is the damping factor specified by the
user.
The Ff and Fr terms are added by this fix.
Ff is a frictional drag or viscous damping term proportional to the
particle's velocity. The proportionality constant for each atom is
computed as m/damp, where m is the mass of the particle and damp is
the damping factor specified by the user.
Fr is a force due to solvent atoms at a temperature T randomly bumping
into the particle. As derived from the fluctuation/dissipation
theorem, its magnitude is proportional to sqrt(T m / dt damp), where T
is the desired temperature, m is the mass of the particle, dt is the
timestep size, and damp is the damping factor. Random numbers are
used to randomize the direction and magnitude of this force as
described in "(Dunweg)"_#Dunweg, where a uniform random number is used
(instead of a Gaussian random number) for speed.
theorem, its magnitude as shown above is proportional to sqrt(Kb T m /
dt damp), where Kb is the Boltzmann constant, T is the desired
temperature, m is the mass of the particle, dt is the timestep size,
and damp is the damping factor. Random numbers are used to randomize
the direction and magnitude of this force as described in
"(Dunweg)"_#Dunweg, where a uniform random number is used (instead of
a Gaussian random number) for speed.
Note that the thermostat effect of this fix is applied to only the
translational degrees of freedom for the particles, which is an