Wave function or density matrix? Ψ or ρ? Schrödinger or Liouville?
Coherent processes in complex systems require a reliable quantum dynamical description.
The most powerful and accurate tool nowadays is the multi-configurational
time-dependent Hartree approach (MCTDH).
It is a direct wave function (Ψ) description
that allows a numerically exact treatment of hundreds degrees of freedom.
are currently integrate this powerful method in our research.
On the other hand, many ultrafast chemical processes can be described
using a partitioning of the overall system into a relevant part
(the 'system') and the remaining degrees of freedom (the 'bath'), and
the resulting density-matrix (ρ) formalism.
Up to know multi-level Redfield theory has been our working horse:
in this method,
a perturbative (up to the second order) treatment of the system-bath interaction allows for a computational efficiency and
appears, if accurately implemented, to be a very reliable approximation for the description of
ultrafast multilevel dissipative dynamics.
It is very advantageous if only few degrees of freedom
are strongly coupled and mainly determine the system dynamics.