This variable select the dynamics of the gauge field used to apply a finite electric field to periodic systems in time-dependent runs.
The gauge field does not have dynamics. The induced polarization field is zero.
The gauge field follows the dynamic described in
Bertsch et al, Phys. Rev. B 62 7998 (2000).
call parse_variable(namespace, 'GaugeFieldDynamics', OPTION__GAUGEFIELDDYNAMICS__POLARIZATION, this%dynamics)