Speaker
Description
Density functional theory (DFT) based methods have become standard tools for accurately describing core-level spectroscopies in systems ranging from small gas-phase molecules to periodic condensed-phase materials. Within the Kohn-Sham DFT (KS-DFT) framework, core-excited states are commonly treated using linear-response time-dependent DFT (LR-TDDFT). More recently, real-time propagation approaches have emerged which enable the simulation of absorption spectra by Fourier transforming the time-dependent dipole moment generated in response to an external perturbation [1,2].
In this work, core-level spectroscopies are simulated using the real-time TDDFT (RT-TDDFT) implementation in the CP2K set of programs [3]. A protocol is first established for calculating static X-ray absorption spectra (XAS) of gas- and liquid-phase water under periodic boundary conditions. The same computational framework is then extended to capture coupled electron-nuclear dynamics on femtosecond timescale. Finally, time-resolved XAS is obtained by propagating the electronic density from well-defined initial states within CP2K, enabling direct simulation of ultrafast core-level spectroscopic responses.
[1] Pemmaraju, C. D. et al., Velocity-gauge real-time TDDFT within a numerical atomic orbital basis set. Comput. Phys. Commun. 2018, 226, 30-38
[2] Tussupbayev, S. et al., Comparison of Real-Time and Linear-Response Time-Dependent Density Functional Theories for Molecular Chromophores Ranging from Sparse to High Densities of States. J. Chem. Theory Comput. 2015, 11, 1102-1109
[3] Kühne, T. D. et al., CP2K: An electronic structure and molecular dynamics software package - Quickstep: Efficient and accurate electronic structure calculations. J. Chem. Phys. 2020, 152, 194103
