# 3.2. tkwant.leads – Time dependence and boundary conditions for leads¶

 add_voltage(syst, lead, phase) Add a time-dependent voltage to a lead.
 SimpleBoundary(num_buffer_cells) Boundary conditions consisting of N lead unit cells. MonomialAbsorbingBoundary(num_absorb_cells, …) Absorbing boundary conditions consisting of N lead unit cells. GenericAbsorbingBoundary(num_absorb_cells, …) Make an absorbing boundary from a user provided-absorbing potential. automatic_boundary(leads, tmax[, refl_max, …]) Routine to find automatically a boundary condition such that the reflection amplitude $$r$$ for a lead stays below a given value.
 AbsorbingReflectionSolver(lead, …[, params]) Calculate the reflection amplitude $$r$$ for a lead with imaginary absorbing potential. AnalyzeReflection(lead, num_absorb_cells, …) Analyze the the reflection for a lead. AnalyzeReflectionMonomial(lead, …[, params]) Analyze the the reflection for a lead for the special case of a monomial absorbing potential.