Publications:
G. Miao, N. Bellonzi, J. E. Subotnik. An extension of the fewest switches surface hopping algorithm to complex Hamiltonians and photophysics in magnetic fields: Berry curvature and “magnetic” forces, The Journal of Chemical Physics 150, 124101 (2019), https://doi.org/10.1063/1.5088770.
Abstract
We present a preliminary extension of the fewest switches surface hopping (FSSH) algorithm to the case of complex Hamiltonians as appropriate for modeling the dynamics of photoexcited molecules in magnetic fields. We make ansätze for the direction of momentum rescaling, and we account for Berry’s phase effects through “magnetic” forces as applicable in the adiabatic limit. Because Berry’s phase is a nonlocal, topological characteristic of a set of entangled potential energy surfaces, we find that Tully’s local FSSH algorithm can only partially capture the correct physics.
N. Bellonzi, G. Medders, E. Epifanovsky, and J. E. Subotnik. Configuration Interaction Singles with Spin-Orbit Coupling: Constructing Spin-Adiabatic States and Their Analytical Nuclear Gradients,The Journal of Chemical Physics 150, 014106 (2019), https://doi.org/10.1063/1.5045484.
Abstract
For future use in modeling photoexcited dynamics and intersystem crossing, we calculate spin-adiabatic states and their analytical nuclear gradients within configuration interaction singles theory. These energies and forces should be immediately useful for surface hopping dynamics, which are natural within an adiabatic framework. The resulting code has been implemented within the Q-Chem software and preliminary results suggest that the additional cost of including spin-orbit coupling within the singles-singles block is not large.
N. Bellonzi, A. Jain, and J. E. Subotnik. An assessment of mean-field mixed semiclassical approaches: Equilibrium populations and algorithm stability, The Journal of Chemical Physics 144, 154110 (2016), https://doi.org/10.1063/1.4946810.
Abstract
We study several recent mean-field semiclassical dynamics methods, focusing on the ability to recover detailed balance for long time (equilibrium) populations. We focus especially on Miller and Cotton’s [J. Phys. Chem. A 117, 7190 (2013)] suggestion to include both zero point electronic energy and windowing on top of Ehrenfest dynamics. We investigate three regimes: harmonic surfaces with weak electronic coupling, harmonic surfaces with strong electronic coupling, and anharmonic surfaces with weak electronic coupling. In most cases, recent additions to Ehrenfest dynamics are a strong improvement upon mean-field theory. However, for methods that include zero point electronic energy, we show that anharmonic potential energy surfacesoften lead to numerical instabilities, as caused by negative populations and forces. We also show that, though the effect of negative forces can appear hidden in harmonic systems, the resulting equilibrium limits do remain dependent on any windowing and zero point energy parameters.
J. E. Subotnik, A. Jain, B. Landry, A. Petit, W. Ouyang, and N. Bellonzi. Understanding the Surface Hopping View of Electronic Transitions and Decoherence, Annual Review of Physical Chemistry 67, 387 (2016), https://doi.org/10.1146/annurev-physchem-040215-112245.
Abstract
We present a current, up-to-date review of the surface hopping methodology for solving nonadiabatic problems, 25 years after Tully published the fewest switches surface hopping algorithm. After reviewing the original motivation for and failures of the algorithm, we give a detailed examination of modern advances, focusing on both theoretical and practical issues. We highlight how one can partially derive surface hopping from the Schrödinger equation in the adiabatic basis, how one can change basis within the surface hopping algorithm, and how one should understand and apply the notions of decoherence and wavepacket bifurcation. The question of time reversibility and detailed balance is also examined at length. Recent applications to photoexcited conjugated polymers are discussed briefly.