Calculation of Non-Adiabatic Couplings in Density-Functional Theory

Copyright © (2005) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics

This paper proposes methods for calculating the derivative couplings between adiabatic states in density-functional theory (DFT) and compares them with each other and with multiconfigurational self-consistent field (MCSCF) calculations. They are shown to be accurate and, as expected, the costs of their calculation scale more favorably with system size than post-Hartree-Fock calculations. The proposed methods are based on single-particle excitations and the associated Slater transition-state densities to overcome the problem of the unavailability of multi-electron states in DFT which precludes a straightforward calculation of the matrix elements of the nuclear gradient operator. An iterative scheme employing linear-response theory was found to offer the best tradeoff between accuracy and efficiency. The algorithms presented here have been implemented for doublet-doublet excitations within a plane-wave-basis and pseudopotential framework but are easily generalizable to other excitations and basis sets. Owing to their fundamental importance in cases where the Born--Oppenheimer separation of motions is not valid, these derivative couplings can facilitate, for example, the treatment of non-adiabatic charge transfers, of electron-phonon couplings, and of radiationless electronic transitions in DFT.

By: Salomon R. Billeter; Alessandro Curioni

Published in: Journal of Chemical Physics, volume 122, (no ), pages 034105-1 in 2005

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