The implementation of a self-consistent constricted variational density functional theory for the description of excited states

We present here the implementation of a self-consistent approach to the calculation of excitation energies within regular Kohn-Sham density functional theory. The method is based on the n-order constricted variational density functional theory (CV(n)-DFT) [T. Ziegler, M. Seth, M. Krykunov, J. Autschbach, and F. Wang, J. Chem. Phys. 130, 154102 (2009)] and its self-consistent formulation (SCF-CV(infinity)-DFT) [J. Cullen, M. Krykunov, and T. Ziegler, Chem. Phys. 391, 11 (2011)]. A full account is given of the way in which SCF-CV(infinity)-DFT is implemented. The SCF-CV(infinity)-DFT scheme is further applied to transitions from occupied pi orbitals to virtual pi* orbitals. The same series of transitions has been studied previously by high-level ab initio methods. We compare here the performance of SCF-CV(infinity)-DFT to that of time dependent density functional theory (TD-DFT), CV(n)-DFT and Delta SCF-DFT, with the ab initio results as a benchmark standard. It is finally demonstrated how adiabatic TD-DFT and Delta SCF-DFT are related through different approximations to SCF-CV(infinity)-DFT. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3696967]