Relativistic Orbital Optimized Density Functional Theory for Accurate Core-Level Spectroscopy

• Published in: arXiv.org
• Main Authors: Cunha, Leonardo A, Hait, Diptarka, Kang, Richard, Mao, Yuezhi, Head-Gordon, Martin
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 30.03.2022
• Subjects: Density functional theory; Electrons; Microprocessors; Periodic table; Physics - Atomic and Molecular Clusters; Physics - Chemical Physics; Physics - Other Condensed Matter; Physics - Quantum Physics; Relativistic effects; Root-mean-square errors; Spectra; Spectrum analysis; Transition metals
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2111.08405

Core-level spectra of 1s electrons of elements heavier than Ne show significant relativistic effects. We combine advances in orbital optimized DFT (OO-DFT) with the spin-free exact two-component (X2C) model for scalar relativistic effects, to study K-edge spectra of third period elements. OO-DFT/X2C is found to be quite accurate at predicting energies, yielding \(\sim 0.5\) eV RMS error vs experiment with the modern SCAN (and related) functionals. This marks a significant improvement over the \(>50\) eV deviations that are typical for the popular time-dependent DFT (TDDFT) approach. Consequently, experimental spectra are quite well reproduced by OO-DFT/X2C, sans empirical shifts for alignment. OO-DFT/X2C combines high accuracy with ground state DFT cost and is thus a promising route for computing core-level spectra of third period elements. We also explored K and L edges of 3d transition metals to identify limitations of the OO-DFT/X2C approach in modeling the spectra of heavier atoms.