Eur. Phys. J. B (2016) 89: 113
https://doi.org/10.1140/epjb/e2016-60702-x

Regular Article

Electronic structure and correlations of vitamin B₁₂ studied within the Haldane-Anderson impurity model

¹ Department of Physics, Izmir Institute of Technology, 35430 Urla, Turkey
² Department of Materials Science and Engineering, Izmir Institute of Technology, 35430 Urla, Turkey

^a e-mail: nejatbulut@iyte.edu.tr

Received: 26 August 2015
Received in final form: 5 March 2016
Published online: 2 May 2016

Abstract

We study the electronic structure and correlations of vitamin B₁₂ (cyanocobalamine) by using the framework of the multi-orbital single-impurity Haldane-Anderson model of a transition-metal impurity in a semiconductor host. The parameters of the effective Haldane-Anderson model are obtained within the Hartree-Fock (HF) approximation. The quantum Monte Carlo (QMC) technique is then used to calculate the one-electron and magnetic correlation functions of this effective model. We observe that new states form inside the semiconductor gap found by HF due to the intra-orbital Coulomb interaction at the impurity 3d orbitals. In particular, the lowest unoccupied states correspond to an impurity bound state, which consists of states from mainly the CN axial ligand and the corrin ring as well as the Co e_g-like orbitals. We also observe that the Co (3d) orbitals can develop antiferromagnetic correlations with the surrounding atoms depending on the filling of the impurity bound states. In addition, we make comparisons of the HF+QMC data with the density functional theory calculations. We also discuss the photoabsorption spectrum of cyanocobalamine.