  Despite enormous experimental and theoretical efforts, obtaining generally
accepted conclusions regarding the intrinsic magnetic and electronic properties
of superconducting nickelates remains exceptionally challenging. Experiments
show a significant degree of uncertainty, indicating hidden factors in the
synthesized films, which call for further investigations. One of those "hidden
factors" is the possibility of intercalating hydrogen during the chemical
reduction process from Nd(La)NiO$_3$ to Nd(La)NiO$_2$ using CaH$_2$. While
hydrogen has been detected in experimental samples, not much is known about its
distribution through the crystal and its influence on the electronic
environment. Here, we show the tendency toward the formation of one-dimensional
hydrogen chains in infinite-layers LaNiO$_2$ superconductors using
density-functional theory (DFT) supplemented by dynamical mean-field theory
(DMFT). The formation of such hydrogen chains induces a coexistence of
different oxidation states of Ni and competing magnetic phases, and possibly
explains the recently observed charge order states in nickelate
superconductors. Furthermore, it contributes to the difficulty of synthesizing
homogeneous nickelates and determining their ground states. The smoking gun to
detect excess hydrogen in nickelates are flat phonon modes, which are infrared
active and quite insensitive to the exact arrangement of the H atoms.
