Reproducibility in LR-TDDFT: The Importance of The Continuum of Unoccupied Orbitals

The reproducibility of DFT results was addressed recently [1], and other areas of computational physics and chemistry could benefit from the same type of study. As a method building on top of DFT, Linear-Response Time-Dependent DFT (LR-TDDFT) [2] is a potential candidate for such studies. In a typical LR-TDDFT calculation, the inclusion of the continuum of unoccupied orbitals is required, and we will see that this is not without raising difficulties when comparing the results of different codes. We will eventually show that the convergence of LR-TDDFT spectra is only possible over a finite range of energy that depends on the system under consideration. This conclusion allows for a meaningful study of the reproducibility of LR-TDDFT calculations.

[1] K. Lejaeghere et al., Science 351 (2016)
[2] M. E. Casida, Recent Advances in Density Functional Methods vol. 1 (1995)