Ultrasoft pseudopotentials in time-dependent density-functional theory

We describe an efficient formulation allowing the use of ultrasoft pseudopotentials (USPPs) in plane wave based time-dependent density-functional theory. The practical steps required to implement USPP functionality within real time propagation schemes and linear-response schemes based on Lanczos algorithms are provided. The functioning of the methodology is demonstrated by calculations of the optical absorption spectra of the fullerene C-60, using both real time propagation and the Lanczos/linear-response approaches. Comparisons between the rates of convergence of the optical spectra with the number of applications of the Hamiltonian required in calculations with ultrasoft pseudopotentials and norm-conserving pseudopotentials show clearly the benefits provided by the use of USPP. (C) 2007 American Institute of Physics.