where the random force 
is derived from a Gaussian
distribution with the properties
where 
is Boltzmann's constant and 
is the temperature specified
by TBATh. For Langevin heatbath applications,
the total energy 
can be augmented
by a harmonic energy term
for all atoms with a nonzero friction coefficient 
.
The setup of the harmonic energy is described in
Section 7.1.
The friction coefficient 
is defined by assigning the
FBETa atom property (see Section 2.16).
Langevin dynamics is used for all atoms that have nonzero
friction coefficients 
and that are outside a sphere
with radius RBUF (default 0)
around the origin ORIGIn. This check is
carried out periodically (ILBFrq parameter). By default
the atom property FBETa is zero;
i.e., all atoms are treated as normal
particles.