Testing TDDFT

The vertical excitation energies were calculated for different configurations of a QM/MM trajectory using the approximate ROKS [27] method as well as TDDFT. The effect of the size of the quantum region was tested systematically by including (i) only the solute in the quantum region or (ii) the solute and its first solvation shell (defined as the 12 water molecules closest to the acetone molecule). 

In view of the potential application of TDDFT methods to the spectroscopy of bioinorganic systems, the dependence of the excitation energies on the exchange-correlation functional and the basis set was carefully tested. In Table 16, the TDDFT results are compared to the known experimental data for the Q and B bands of CO-ligated mioglobin (Mb) [163], the SAC-CI calcula-... 

We showed that TDDFT excited-state MD simulations can provide interesting insights into photoreactions, but the correct description of the excited-state PES has to be carefully tested. 

In these practical calculations, both the ground-state XC potential and TDDFT XC kernel are approximated. A simple way to separate the error in the XC kernel is to examine a test case where the exact KS potential is known. Figure 5 shows the spectrum of He using the exact KS potential, but with the ALDA XC kernel. The ALDA XC kernel does rather welP (very well, as we shall see later when we examine atoms in more detail), and very similar results are obtained with standard GGAs. 

After initial testing on small systems, Chelikowsky s group extended their real-space code (now called PARSEC) for a wide range of challenging applications.The applications include quantum dots, semiconductors, nanowires, spin polarization, and molecular dynamics to determine photoelectron spectra, metal clusters, and time-dependent DFT (TDDFT) calculations for excited-state properties. PARSEC calculations have been performed on systems with more than 10,000 atoms. The PARSEC code does not utilize MG methods but rather employs Chebyshev-filtered subspace acceleration and other efficient techniques during the iterative solution process. When possible, symmetries may be exploited to reduce the numbers of atoms treated explicitly. 

---