Density Functional Resonance Theory: complex density functions, convergence, orbital energies, and functionals

TL;DR

This paper explores the detailed properties and practical implementation considerations of Density Functional Resonance Theory (DFRT), a complex-scaled extension of DFT, focusing on complex densities, energies, and decay behaviors.

Contribution

It provides a comprehensive analysis of DFRT's asymptotic behavior, implementation sensitivities, and relationships between Kohn-Sham and physical system energies and thresholds.

Findings

Complex density functions relate to resonance energies and decay directions.

Proper basis sets reduce θ-dependence in energies and lifetimes.

Kohn-Sham orbital energies connect to physical affinities and widths.

Abstract

Aspects of Density Functional Resonance Theory (DFRT) [Phys. Rev. Lett. \textbf{107}, 163002 (2011)], a recently developed complex-scaled version of ground-state Density Functional Theory (DFT), are studied in detail. The asymptotic behavior of the complex density function is related to the complex resonance energy and system's threshold energy, and the function's local oscillatory behavior is connected with preferential directions of electron decay. Practical considerations for implementation of the theory are addressed including sensitivity to the complex-scaling parameter, $\theta$. In Kohn-Sham DFRT, it is shown that almost all $\theta$-dependence in the calculated energies and lifetimes can be extinguished via use of a proper basis set or fine grid. The highest occupied Kohn-Sham orbital energy and lifetime are related to a physical affinity and width, and the threshold energy of the Kohn-Sham system is shown to be equal to the threshold energy of the interacting system shifted by a well-defined functional. Finally, various complex-scaling conditions are derived which relate the functionals of ground-state DFT to those of DFRT via proper scaling factors and a non-Hermitian coupling constant system.