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
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 T matches .