Fritz Haber Seminar: Alexey Akimov, University at Buffalo, New York

14 January, 2021

Modeling Nonadiabatic Dynamics in Nanoscale Solar Energy Materials
Alexey Akimov, Dept. of Chemistry, University at Buffalo, NY, USA
4 PM via Zoom:

The dynamics of excited states is critically important in many materials such as photovoltaic solar energy harvesters, photocatalysts, or photo-actuated molecular switches. Electron-hole recombination, interfacial charge transfer, or nonradiative excitation energy relaxation, all require accounting for nonadiabatic (NA) effects. Computational modeling of NA and quantum dynamics (NA/QD) at the atomistic level can provide valuable insights into these processes and help design new routes for improving materials' efficiencies, but also poses a great challenge to the scientific community due to its taxing computational complexity. The demands for modeling NA/QD in periodic solids and nanoclusters stimulated the development of numerous approximations and the wide adoption of simplified computational schemes. However, the quality of such schemes remains largely unclear, leaving one questioning about their applicability. It is often unclear how one scheme compares with another in a zoo of many ad hoc approaches.

With the idea of facilitating the assessment of various NA/QD schemes, my group developed a modular open-source Libra software1 and utilized it as a framework for developing new practical tools for NA/QD, assessing a variety of existing approximations, and for applied studies of NA dynamics in various types of nanoscale solar energy materials. In this presentation, I will discuss some of our recent developments for the approximate modeling of NA/QD in nanoscale and condensed-matter systems. First, I will demonstrate how the Landau-Zener-inspired trajectory surface hopping approach can aid in modeling hot carrier relaxation dynamics in Si nanocrystals/quantum dots and help reveal qualitative trends on relaxation rates as a function of the nanoparticles' size and surface termination type.2 I will then proceed to our recently developed schemes that can account for some many-body effects in modeling NA/QD in nanocrystals3 and periodic solids.4


(1)   Akimov, A. V. Libra: An Open-Source “Methodology Discovery” Library for Quantum and Classical Dynamics Simulations. J. Comput. Chem. 2016, 37, 1626–1649.

(2)   Smith, B.; Akimov, A. V. Hot Electron Cooling in Silicon Nanoclusters via Landau–Zener Nonadiabatic Molecular Dynamics: Size Dependence and Role of Surface Termination. J. Phys. Chem. Lett. 2020, 11, 1456–1465.

(3)   Smith, B. A.; Shakiba, M.; Akimov, A. V. Nonadiabatic Dynamics in Si and CdSe Nanocluster: Many-Body vs. Single-Particle Treatment of Excited States. J. Chem. Theory Comput. 2021. (just accepted)

(4)   Smith, B. A.; Shakiba, M.; Akimov, A. V. Crystal Symmetry and Static Electronic Correlation Greatly Accelerate Nonradiative Dynamics in Lead Halide Perovskites. J. Phys. Chem. Lett. 2021. (under review)

(5)   Lin, Y.; Akimov, A. V. Dependence of Nonadiabatic Couplings with Kohn–Sham Orbitals on the Choice of Density Functional: Pure vs Hybrid. J. Phys. Chem. A 2016, 120, 9028–9041.

(6)   Li, W.; Zhou, L.; Prezhdo, O. V.; Akimov, A. V. Spin–Orbit Interactions Greatly Accelerate Nonradiative Dynamics in Lead Halide Perovskites. ACS Energy Lett. 2018, 3, 2159–2166.

(7)   Smith, B., A.; Akimov, A. V. A Comparative Analysis of Surface Hopping Acceptance and Decoherence Algorithms within the Neglect of Back-Reaction Approximation. J. Chem, Phys. 2019, 151, 124107.