The state-specific approach to the solution of problems of electronic structure and dynamics involving excited states

If, in conjunction with suitable computational methods, attention is given to the state-specific choice and optimization of function spaces, especially when studying excited states, the accuracy of the description of electronic structure and of the results of computation of properties increases, while the complexity of the many-electron problem is reduced significantly. These facts allow the consistent understanding of the interplay between major features of electronic structure and properties or processes, as well as the practical numerical solution of computationally very demanding problems (e.g., solution of the multielectron time-dependent Schrödinger equation). This is the conclusion from a number of applications of the state-specific approach (SSA) to the analysis and calculation of stationary and nonstationary states, in the absence or presence of external electromagnetic fields. A review is given of the basic features of the various formalisms that have been employed within the SSA for the solution of problems of electronic structure and dynamics. In addition, I comment, via specific examples, on the computation of the Fermii-Sea wavefunctions for strongly mixed states and of valence-Rydberg-continuum interactions.