This option is turned on by TCOUpling.
This method
was described by
Berendsen et al. (1984). It is essentially a Langevin-type
method with zero random forces and a scaled friction
coefficient.
The friction coefficient
is computed by the program from the equation

(11.7)

where is given by the FBETa atom property.
Note that FBETa is by default zero; i.e., FBETa has to be
specified in order to use TCOUpling.
The target temperature is specified by the TBATh parameter.
is the
temperature of the system at
the particular step where is the number of degrees of freedom of
the system. Thus, a positive fricition coefficient is applied
if the system is too hot, a negative friction coefficient is
applied if the system is too cold, and no friction is applied if
matches .