Combined self-consistent DFT+U and Quantum Monte Carlo investigation of the High Pressure Spin Transition in Ferropericlase

Ferropericlase (Mg_1-x,Fe_x)O (0<x<1) is a transition metal oxide that undergoes an antiferromagnetic high spin to nonmagnetic low spin transition at high pressure. Due to the strong correlation of the Fe 3d electrons, common semi-local exchange-correlation functionals such as LDA, PBE, & etc. fail to accurately capture the ground state properties such as a finite bandgap, magnetic structure, and equation of state. For this reason, extensions such as DFT+U have traditionally been used, but can be subject to metastable solutions and other limitations. Here we use a self-consistently calculated LDA+U approach to generate trial wave functions for subsequent diffusion quantum Monte Carlo calculations to investigate the ground state properties and spin transition in ferropericlase using an explicitly many-body method that more accurately captures electron correlations. The results will be used to guide future experiments on the Z Machine at Sandia National Laboratories. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.