Non-Born–Oppenheimer Dynamics and Conical Intersections
The area of excited-state dynamics is receiving increasing attention for a number of reasons. First the importance of photochemical processes in basic energy sciences, improved theoretical methods and the associated theoretical understanding of photochemical processes. Then there is the advent of femtosecond (and now attosecond) spectroscopy allowing access to more detailed experimental information about photochemical processes. Since photophysical and chemical processes are more complex than thermal (i.e., ground state) processes, simulations quickly become expensive and even unmanageable as the model system becomes increasingly realistic. With its combination of simplicity and yet relatively good accuracy, TDDFT has been finding an increasingly important role to play in this rapidly developing field. After reviewing some basic ideas from photophysics and photochemistry, this chapter will cover some of the strengths and weaknesses of TDDFT for modeling photoprocesses.