Excitonic effects in time-dependent density functional theory from zeros of the density response

We show that the analytic structure of dynamical exchange-correlation (xc) kernels semiconductors and insulators can be sensed in terms its poles, which mark physically relevant frequencies system where counterphase motion discrete collective excitations occurs: If excited, modes counterbalance each other, making exhibit none at all or extremely weak density response. This property employed to construct simple practically approximations xc kernel for time-dependent functional theory (TDDFT). Such have structures, are able reproduce dominant excitonic features absorption spectra monolayer bulk solids, promise high potential future uses efficient real-time calculations with TDDFT.