TY - JOUR
KW - paper
AU - P. Romaniello
AU - D Sangalli
AU - J Berger
AU - Francesco Sottile
AU - L. Molinari
AU - Lucia Reining
AU - G Onida
AB - Time-dependent density-functional theory \textquoterightTDDFT\textquoteright is widely used in the study of linear response properties of finite systems. However, there are difficulties in properly describing excited states, which have double- and higher-excitation characters, which are particularly important in molecules with an open-shell ground state. These states would be described if the exact TDDFT kernel were used; however, within the adiabatic approximation to the exchange-correlation fxc kernel, the calculated excitation energies have a strict single-excitation character and are fewer than the real ones. A frequency-dependent xc kernel could create extra poles in the response function, which would describe states with a multiple-excitation character. We introduce a frequency-dependent xc kernel, which can reproduce, within TDDFT, double excitations in finite systems. In order to achieve this, we use the Bethe\textendashSalpeter equation with a dynamically screened Coulomb interaction W, which can describe these excitations, and from this we obtain the xc kernel. Using a two-electron model system, we show that the frequency dependence of W does indeed introduce the double excitations that are instead absent in any static approximation of the electron-hole screening.
BT - Journal of Chemical Physics
DO - 10.1063/1.3065669
N2 - Time-dependent density-functional theory \textquoterightTDDFT\textquoteright is widely used in the study of linear response properties of finite systems. However, there are difficulties in properly describing excited states, which have double- and higher-excitation characters, which are particularly important in molecules with an open-shell ground state. These states would be described if the exact TDDFT kernel were used; however, within the adiabatic approximation to the exchange-correlation fxc kernel, the calculated excitation energies have a strict single-excitation character and are fewer than the real ones. A frequency-dependent xc kernel could create extra poles in the response function, which would describe states with a multiple-excitation character. We introduce a frequency-dependent xc kernel, which can reproduce, within TDDFT, double excitations in finite systems. In order to achieve this, we use the Bethe\textendashSalpeter equation with a dynamically screened Coulomb interaction W, which can describe these excitations, and from this we obtain the xc kernel. Using a two-electron model system, we show that the frequency dependence of W does indeed introduce the double excitations that are instead absent in any static approximation of the electron-hole screening.
PY - 2009
EP - 044108
T2 - Journal of Chemical Physics
TI - Double excitations in finite systems
UR - http://dx.doi.org/10.1063/1.3065669
VL - 130
ER -