  We study the spin-crossover molecule Fe(phen)$_2$(NCS)$_2$ 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 realistic interaction
parameters. Comparisons to DFT and DFT+U calculations demonstrate that
dynamical correlations are critical to the energetics of the low-spin state.
Additionally, we elucidate the differences between DFT+U and spin density
functional theory (SDFT) plus U methodologies, demonstrating that DFT+U can
recover SDFT+U results for an appropriately chosen on-site exchange
interaction.
