What advanced quantum many-body methods teach us about molecular magnetism

Prof Jurgen Schnack, Faculty of Physics, Bielefeld University, Germany

Three powerful approximations of the Schrödinger equations have been developed in the 1990s: Quantum Monte Carlo (QMC), Density Matrix Renormalization Group (DMRG) and the Finite-Temperature Lanczos Method (FTLM). These three methods are nowadays applied not only in condensed matter physics, but also in nuclear physics and quantum chemistry. In my talk I am going to show how thermodynamic observables of magnetic molecules can be evaluated for Hilbert space dimensions of up to 1010 with unprecedented accuracy by employing and generalizing FTLM [1]. The influence of intermolecular interactions on the behaviour of magnetic molecules, which so far was estimated using mean field approaches, can today be evaluated quasi exactly using QMC for bipartite arrangements of spins [2]. DMRG and Dynamical DMRG (DDMRG) allow us to understand spectra of inelastic neutron scattering [3], but I might swap this topic in favour of explaining what the Numerical Renormalization Group (NRG) tells us about the modification of Kondo impurities on metallic substrates.

[1] O. Hanebaum, J. Schnack, Thermodynamic observables of Mn12-acetate calculated for the full spin-Hamiltonian, Phys. Rev. B 92 (2015) 064424
[2] J. Schnack, Influence of intermolecular interactions on magnetic observables,
Phys. Rev. B 93 (2016) 054421
[3] J. Ummethum, J. Nehrkorn, S. Mukherjee, N. B. Ivanov, S. Stuiber, Th. Strässle, P. L. W. Tregenna-Piggott, H. Mutka, G. Christou, O. Waldmann, J. Schnack, Discrete antiferromagnetic spin-wave excitations in the giant ferric wheel Fe18,
Phys. Rev. B 86 (2012) 104403

Host: Prof Steve Blundell

Audrey Wood Seminar Room, Clarendon Laboratory

09.02.17 Jurgen Schnack.pdf110.31 KB