ABSTRACT
In recent years, the density functional theory (DFT) has become a widely used formalism for electron structure calculations of atoms, molecules, and solids [1-5]. The DFT is based on the earlier fundamental work of Hohenberg and Kohn [6] and Kohn and Sham [7]. In the Kohn-Sham DFT formalism [7], the electron density is decomposed into a set of orbitals, leading to a set of one-electron Schrödinger-like equations to be solved self-consistently. The Kohn-Sham equations are structurally similar to the Hartree-Fock equations but include, in principle, exactly many-body effects through a local exchange-correlation (xc) potential. Thus, DFT is computationally much less expensive than traditional ab initio many-electron wavefunction approaches, and this accounts for its great success for large systems. However, the DFT is well developed mainly for the ground-state properties only. The treatment of excited states and timedependent processes within the DFT is relatively less developed.
