Towards a primer on close proximity of hydrogen atoms in metal lattices

There is wide consensus that close proximity <0.1 nm of hydrogen isotopes (such as deuterium pairs) is likely an important precondition for hypothesized low-energy nuclear reactions (LENR) effects to take place. This is also the case in our New J. Physics paper, where section S6.21 in particular discusses relevant aspects of hydrogen in a Pd lattice. In our rate calculations, the Coulomb barrier shows up as a hindrance factor that slows down transitions of interest. And the larger the distance between deuterons, the greater that hindrance factor. Consequently, we are interested under what conditions close proximity of hydrogen isotopes is possible in metal lattices. 

This issue relates to a number of subfields of the literature on metal hydrides, not all of which are closely connected. Key issues are:

• The study of stable phases of different metal hydrides under different temperature and pressure conditions and the geometry of such phases
• The formation of defects such as vacancies and the conditions that favor them
• The diffusion of hydrogen atoms as well as the diffusion of defects through metal hydrogen lattices
• The site occupation of 
• The behavior of hydrogen atoms and molecules vis-a-vis metal surfaces, including the breakup of molecules and the formation of complex molecular structures such as di-hydrogen and di-deuterium structures

This post serves as a place to capture such key issues along with particularly instructive papers and arguments on each of these points. It will be extended over time, so be sure to revisit it.