Photoionization and core resonances from range-separated time-dependent density-functional theory for open-shell states: Example of the lithium atom

TL;DR

This paper develops and applies range-separated time-dependent density-functional theory methods to calculate photoionization spectra and core resonances of open-shell systems, demonstrated on the lithium atom.

Contribution

It introduces TDRSH and TDLRSH schemes with a spin-unrestricted Sternheimer approach for open-shell systems, enhancing computational efficiency and accuracy.

Findings

TDRSH and TDLRSH effectively estimate photoionization spectra.

The methods are suitable for open-shell systems like lithium.

Efficient linear-response calculations are achieved with a B-spline basis.

Abstract

We consider the calculations of photoionization spectra and core resonances of open-shell systems using range-separated time-dependent density-functional theory. Specifically, we use the time-dependent range-separated hybrid (TDRSH) scheme, combining a long-range Hartree-Fock (HF) exchange potential and kernel with a short-range potential and kernel from a local density-functional approximation, and the time-dependent locally range-separated hybrid (TDLRSH) scheme, which uses a local range-separation parameter. To efficiently perform the calculations, we formulate a spin-unrestricted linear-response Sternheimer approach in a non-orthogonal B-spline basis set and using appropriate frequency-dependent boundary conditions. We illustrate this approach on the Li atom, which suggests that TDRSH and TDLRSH are adequate simple methods for estimating single-electron photoionization spectra of open-shell systems.