X-PLOR provides the possibility of carrying out
Langevin dynamics. The simple Langevin equation has the form

(11.2)

where the random force is derived from a Gaussian
distribution with the properties

(11.3)

(11.4)

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.