We study the spin-crossover molecule $\text{Fe}{\left(\mathrm{phen}\right)}_2{\left(\mathrm{NCS}\right)}_2$ using density functional theory (DFT) plus dynamical mean-field theory, which allows access to observables not attainable with traditional quantum chemical or electronic structure methods. The temperature dependent magnetic susceptibility, electron addition and removal spectra, and total energies are calculated and compared to experiment. We demonstrate that the proper quantitative energy difference between the high-spin and low-spin state, as well as reasonably accurate values of the magnetic susceptibility can be obtained when using reasonable interaction parameters. Comparisons to DFT and $\text{DFT}+U$ calculations demonstrate that dynamical correlations are critical to the energetics of the low-spin state. Additionally, we elucidate the differences between $\text{DFT}+U$ and spin density functional theory (SDFT) plus $U$ methodologies, demonstrating that $\text{DFT}+U$ can recover $\text{SDFT}+U$ results for an appropriately chosen on-site exchange interaction.

• Received 11 March 2015
• Revised 21 May 2015

DOI:https://doi.org/10.1103/PhysRevB.91.241111