We determine the nature of the magnetic quantum critical point in the doped LaFeAsO using a set of constrained density functional calculations that provide ab initio coefficients for a Landau order parameter analysis. The system turns out to be remarkably close to a quantum tricritical point, where the nature of the phase transition changes from first to second order. We compare with the effective field theory and discuss the experimental consequences.
@article{arxiv.1009.0009,
title = {Proximity of Iron Pnictide Superconductors to a Quantum Tricritical Point},
author = {G. Giovannetti and C. Ortix and M. Marsman and M. Capone and J. van den Brink and J. Lorenzana},
journal= {arXiv preprint arXiv:1009.0009},
year = {2012}
}