Abstract

The talk will focus on complexes of 3d transition metal atoms ( TM ) with benzene molecule(s). These systems represent one of the most important families of π-bonded organometallics. Among the most important and intriguing applications is the use of sandwich-type TM-benzenes as spin valves, featuring system-size dependent metallic behavior for the majority spin electrons and a semiconductor gap for the minority spin electrons [1]. We will present accurate quantum Monte Carlo (QMC) calculations [2] which enabled us to determine the structure, spin multiplicity, ionization energy, dissociation energy, and spin-dependent electronic gaps of the short-sandwich vanadium- and cobalt-benzene systems and their cations. For this purpose we have used a multi-stage combination of techniques with consecutive elimination of all systematic biases except for the fixed-node approximation in QMC . Our calculations illustrate the scatter and significant differences in DFT spin multiplicities and dissociation energies which sensitively depend on the used exchange-correlation functional. Hence, our results significantly differ from the established picture based on less accurate calculations (gradient corrected, hybrid, meta hybrid, and double hybrid DFT ). The results enabled us to reveal the DFT biases which are of the order of ≈0.5 eV. At the same time our study exposes the shortcomings and biases of the existing experimental results and point out the importance of high-level many-body methods for predictive calculations of similar TM-based organometallic systems.

1. V. V. Maslyuk et al., Phys. Rev. Lett. 97, 097201 (2006).
2. L. Horváthová, M. Dubecký, L. Mitas, and I. Štich, Phys. Rev. Lett. 109, 053001 (2012).