DENSITY-FUNCTIONAL-THEORY RESPONSE-PROPERTY CALCULATIONS WITH ACCURATE EXCHANGE-CORRELATION POTENTIALS

Response calculations in the framework of time-dependent density-funct ional theory (TDDFT) have by now been shown to surpass time-dependent Hartree-Fock (TDHF) calculations in both accuracy and efficiency. This makes TDDFT an important tool for the calculation of frequency-depend ent (hyper)polarizabilities, excitation energies, and related properti es of medium-sized and large molecules. Two separate approximations ar e made in the linear DFT response calculations. The first approximatio n concerns the exchange-correlation (xc) potential, which determines t he form of the Kohn-Sham orbitals and their one-electron energies, whi le the second approximation involves the so-called xc kernel f(xc), wh ich determines the re contribution to the frequency-dependent screenin g. By performing calculations on small systems with accurate re potent ials, constructed from ab initio densities, we can test the relative i mportance of the two approximations for different properties and syste ms, thus showing what kind of improvement can be expected from future, more refined, approximations to these re functionals. We find that in most, but not all, cases, improvements to nu(xc) seem more desirable than improvements to f(xc).