  The ability to accurately predict the finite temperature properties of
realistic quantum solids is central to uncovering new phases and engineering
materials with novel properties. Nonetheless, there remain comparatively few
many-body techniques capable of elucidating the finite temperature physics of
solids from first principles. In this work, we take a significant step towards
developing such a technique by generalizing our previous, fully ab initio
finite temperature Auxiliary Field Quantum Monte Carlo (FT-AFQMC) method to
model periodic solids and employing it to uncover the finite temperature
physics of periodic hydrogen chains. Based upon our calculations of these
chains' many-body thermodynamic quantities and correlation functions, we
outline their metal-insulator and magnetic ordering as a function of both H-H
bond distance and temperature. At low temperatures approaching the ground
state, we observe both metal-insulator and ferromagnetic-antiferromagnetic
crossovers at bond lengths between 0.5 and 0.75 {\AA}. We then demonstrate how
this low-temperature ordering evolves into a metallic phase with decreasing
magnetic order at higher temperatures. By comparing the features we observe to
those previously seen in one-dimensional, half-filled Hubbard models at finite
temperature and in ground state hydrogen chains, interestingly, we identify
signatures of the Pomeranchuk effect in hydrogen chains for the first time and
show that spin and charge excitations that typically arise at distinct
temperatures in the Hubbard model are indistinguishably coupled in these
systems. Beyond qualitatively revealing the many-body phase behavior of
hydrogen chains, our efforts shed light on the further theoretical developments
that will be required to construct the phase diagrams of the more complex
transition metal, lanthanide, and actinide solids of longstanding interest to
physicists.
