A precaution for the hybrid density functional calculation of open-shell systems

TL;DR

This paper highlights the importance of incorporating spin dependence in hybrid density functional calculations for open-shell systems to avoid significant self-interaction errors, demonstrated through molecular and crystalline examples.

Contribution

It reveals that ignoring spin dependence in hybrid density functional calculations leads to substantial errors in open-shell systems, emphasizing the need for spin-aware approaches.

Findings

Ignoring spin dependence causes large errors in ionization potential calculations.

Including spin dependence reduces self-interaction errors.

Results show improved accuracy with spin-dependent hybrid functionals.

Abstract

We show that a naive treatment of open-shell systems in hybrid density functional calculations ignoring the spin dependence causes significant errors due to a kind of self interaction that is not emerged in spin-dependent calculations. As numerical examples, we compare the results of the LDA, GGA, and PBE0 calculations on the ionization potential and electron affinity of C$_{60}$ molecule and the GGA and HSE calculations on the singly charged monovacancy in crystalline Si.