Efficient Implementation of RT-TDDFT on Siesta 4.0*

Real-time time-dependent DFT (RT-TDDFT) provides a versatile method for computing electronic response in both linear and non-linear regimes. Here we introduce RT-Siesta4, an efficient implementation of RT-TDDFT which combines the LCAO approach for electronic structure in Siesta 4.0 with an efficient Crank-Nicolson time-evolution operator to propagate Kohn-Sham states in the presence of an external electric field. This development extends our previous implementation with Siesta 2.0.¹ RT-Siesta4 uses a predictor-corrector scheme to ensure time-reversibility, thus enabling long time steps. Its capabilities include full spectrum linear optical response, single frequency NLO response, and response to shaped pulses. Benchmarks for typical systems are presented showing how the faster evaluation of the TD Hamiltonian in Siesta 4.0 improves the performance of our real-time implementation. Finally, we discuss the need to extend scalability into the peta- and exa-scales.
[1] Y. Takimoto et al., J. Chem. Phys. 127, 154114 (2007).