Defining scripted biases

Rather than using the biasing methods described above, it is possible to apply biases provided at run time as a Tcl script. This option, also available in NAMD, can be useful to test a new algorithm to be used in a MD simulation.

• scriptedColvarForces $\langle\,$ Enable custom, scripted forces on colvars $\,\rangle$
  Context: global
  Acceptable values: boolean
  Default value: off
  Description: If this flag is enabled, a Tcl procedure named calc_colvar_forces accepting one parameter should be defined by the user. It is executed at each timestep, with the current step number as parameter, between the calculation of colvars and the application of bias forces. This procedure may use the cv command to access the values of colvars (e.g. cv colvar xi value), apply forces on them (cv colvar xi addforce $F) or add energy to the simulation system (cv addenergy $E), effectively defining custom collective variable biases.