Real-Time TD-DFT with Classical Ion Dynamics: Methodology and Applications

Abstract

We present a method for real-time propagation of electronic wave functions, within time-dependent density functional theory (RT-TDDFT), coupled to ionic motion through mean-field classical dynamics. The goal of our method is to treat large systems and complex processes, in particular photocatalytic reactions and electron transfer events on surfaces and thin films. Due to the complexity of these processes, computational approaches are needed to provide insight into the underlying physical mechanisms and are therefore crucial for the rational design of new materials. Because of the short time step required for electron propagation (of order ∼10 attoseconds), these simulations are computationally very demanding. Our methodology is based on numerical atomic-orbital-basis sets for computational efficiency. In the computational package, to which we refer as TDAP-2.0 (Time-evolving Deterministic Atom Propagator), we have implemented a number of important features and analysis tools for more accurate and efficient treatment of large, complex systems and time scales that reach into a fraction of a picosecond. We showcase the capabilities of our method using four different examples: (i) photodissociation into radicals of opposite spin, (ii) hydrogen adsorption on aluminum surfaces, (iii) optical absorption of spin-polarized organic molecule containing a metal ion, and (iv) electron transfer in a prototypical dye-sensitized solar cell.

Polaron-induced phonon localization and stiffening in rutile TiO2

“…Our calculation of the lowest charge-neutral excited state within the DFT ∆SCF method [25] yielded excitation energy E ∆SCF g = 3.7 eV in the bulk at T =0 K. After correcting this energy for the spin contamination, [34,35], we obtained E g = 3.4 eV. This agrees very well with the value obtained from BSE calculations (3.3 eV) [36], thus confirming our choice of the value U = 4.2 eV, but overestimates the experimental band gap of 3.03 eV.…”

“…Computational. For the theoretical modeling, in both the adiabatic and non-adiabatic (Ehrenfest dynamics) calculations we use our code TDAP-2.0 [25], which is based on the SIESTA package [26,27], an efficient DFT code employing numerical atomic orbitals (NAO) as the basis set. Following Refs.…”

“…Brillouin zone was sampled at Γ-point, except for smaller supercells used in convergence tests where we used Monkhorst-Pack k-point grids starting from 8 × 8 × 12 for a single unit cell. As in the works prior to this [3,25,31], we used PBE+U functional with U = 4.2 eV in all our calculations. In this study we used standard SIESTA pseudopotentials and SZP basis set.…”

“…We model the polaron using density functional theory (DFT) and probe the dynamics of its formation with real-time time-dependent density functional theory (RT-TDDFT) which employs mean-field classical-ion (Ehrenfest) dynamics to couple the electronic and ionic subsystems [25]. We show that this approach is adequate to capture the dynamics and time scales of formation of small polarons by photo-generated or injected carriers in rutile TiO 2 .…”

Ab initio nonadiabatic molecular dynamics investigations on the excited carriers in condensed matter systems

“…Meng and Kaxiras have included the photoexcitation in the first principle simulations in TDAP. Kaxiras and Kolesov have also developed a similar code TDAP‐2.0 . We expect that emerging research area will attract more and more interests from scientists in physics and chemistry in the future.…”