Spin Multiplicity and Symmetry Breaking in Vanadium-Benzene Complexes

We present accurate quantum Monte Carlo (QMC) calculations which enabled us to determine the structure, spin multiplicity, ionization energy, dissociation energy, and spin-dependent electronic gaps of the vanadium-benzene system. From total and ionization energy we deduce a high-spin state with vastly different energy gaps for the two spin channels. For this purpose we have used a multistage combination of techniques with consecutive elimination of systematic biases except for the fixed-node approximation in QMC calculations. Our results significantly differ from the established picture based on previous less accurate calculations and point out the importance of high-level many-body methods for predictive calculations of similar transition metal-based organometallic systems.

Figure 1

Half-sandwich (top panel) and sandwich-type (lower panel) of structures of TMBz complexes. Schematics of possible Jahn-Teller distortions are shown in the top panel.

Figure 2

Energies, relative to the minimum, of VBz for various spin multiplicities calculated in the DFT and DMC/B3LYP approaches.

Figure 3

Energies, aligned to zero, of VBz for $M=2,4,6$, 4, 6 as a function of the average V-C distance $r$ in DFT-B3LYP (dashed line) and DMC/B3LYP (points with error bars and fit/full line) approaches.