Seems to me that if you squeezed two hydrogen atoms between two or more larger atoms that are relatively inert or have no affinity for hydrogen but do have a large affinity for each other, then the covalent pressure of the ‘squeezers’ would eventually cause the hydrogen nuclei to fuse....................
That is, more or less, what “lattice confinement” is all about.
Group 1 of the Periodic Table represents Alkali Metals, with Hydrogen the least massive, residing at the top. Some chemists place Hydrogen in the Halogen Group. It is a bit oddball, going against the grain in the bonds it forms.
Due to the difficulties encountered in brute-forcing Hydrogen phase transition to the metallic, the characteristics allowing classification as a metal is usually glossed over in practice. The transfer of energy to achieve a lower resting state, so as to display the metallic phase character is problematic. Dynamic application of very high pressure has resulted in transient episodes of high electrical conduction as expected in a metal.
Experiments with heavy alkali metals, which aimed to promote formation of self organizing clusters, established a methodology to transfer excess energy to a second physical body. This process was eventually applied to formation of cluster hydrogen. This “condensation” energy is of the order of one-hundred times typical hydrogen chemical reaction results.
A high density cluster form of hydrogen results, which presents with the Superfluid Fountain and Meissner Effect at above room temperature. This cluster material is metastable with a more dense form, which occasionally has been observed as a seemingly spontaneous transformation.
That ultra dense form is compatible with quantum tunnel activity to achieve deuterium fusion. In other words, do not store in significant quantities, manufacture on a just-in-time use basis.