Fast, accurate enthalpy differences in spin crossover crystals from DFT+U.

Area of Science:

• Materials Science
• Computational Chemistry
• Solid-State Physics

Background:

• Spin crossover (SCO) materials are bi-stable systems with potential applications in molecular electronics and sensors.
• Accurate calculation of the enthalpy difference (ΔH) between high spin (HS) and low spin (LS) states is crucial for predicting SCO behavior.
• Many conventional density functional theory (DFT) methods struggle to accurately predict the sign and magnitude of ΔH.

Purpose of the Study:

• To evaluate the performance of DFT+U methods in calculating ΔH for SCO materials.
• To compare the accuracy of DFT+U with established hybrid functionals like TPSSh.
• To identify a computationally efficient and accurate method for studying SCO phenomena in crystalline materials.

Main Methods:

• Benchmarking DFT functionals using a dataset of Fe(II) and Fe(III) SCO materials with experimentally measured ΔH values.
• Investigating the Liechtenstein and Dudarev formulations of DFT+U.
• Assessing the mean absolute error (MAE) of predicted ΔH values against experimental data.

Main Results:

• The hybrid functional TPSSh achieved a MAE of 11 kJ mol⁻¹.
• Both Liechtenstein and Dudarev DFT+U methods showed improved accuracy over TPSSh.
• The Dudarev DFT+U method, with Ueff = 1.6 eV, yielded a MAE of 8 kJ mol⁻¹.
• Excluding a single outlier material, DFT+U achieved chemical accuracy.

Conclusions:

• DFT+U methods, particularly the Dudarev formulation, offer a promising and accurate approach for calculating ΔH in SCO crystals.
• DFT+U provides accuracy comparable to meta-hybrid functionals but at a significantly lower computational cost.
• This makes DFT+U an attractive choice for large-scale studies of spin crossover phenomena in solid-state materials.