Accurate crystal field Hamiltonians of single-ion magnets at mean-field cost

TL;DR

This paper presents a low-cost density functional theory method to accurately derive effective crystal field Hamiltonians for single-ion magnets, matching expensive quantum chemistry results and reproducing experimental properties.

Contribution

A simple, cost-effective approach using density functional calculations to obtain accurate crystal field Hamiltonians for single-ion magnets.

Findings

Matches multi-configurational quantum chemistry results

Reproduces experimental spectra and magnetic properties

Operates at mean-field computational cost

Abstract

The effective crystal field Hamiltonian provides the key description of the electronic properties of single-ion magnets, but obtaining its parameters from ab initio computation is challenging. We introduce a simple approach to derive the effective crystal field Hamiltonian through density functional calculations of randomly rotated mean-field states within the low-energy manifold. In benchmarks on five lanthanide-based complexes, we find that we compute with mean-field cost an effective crystal field Hamiltonian that matches the state-of-the-art from much more expensive multi-configurational quantum chemistry methods. In addition, we are able to reproduce the experimental low-energy spectrum and magnetic properties with an accuracy exceeding prior attempts. Due to its low cost, our approach provides a crucial ingredient in the computational design of single-ion magnets with tailored physical properties and low-energy spectra.