Nature and Science will want an original result. Physical Review (B) or PRL are likely too high ranked as well. Put it in some place like J. Appl. Physics or Chemistry of Materials or J Chem Phys or Materials Theory or the like. (I don't know the specifics...of course if it involves ceramics those journals are a good fit; if it involves bio, those are good.)
I would encourage you to get it into a real journal (not Arxive). Something like a specialty APS or ACS journal. The archival is superior...ends up being put on acid-free paper and retained for hundreds of years in Harvard library. Digital storage and version control are not as good as dead trees. In addition going through peer review and a copy editor ends up almost all the time pushing a more professional product with lesser typos and the like.
I wouldn't underestimate the difficulty involved in doing what you are trying to do. For one thing the materials journal has to a bit take on faith the math efficacy (or repeat the review of that). But it's not impossible.
Also, try to show some example system and some charts versus temperature or instrument resolution or the like (even if no experiments, just "drawing spaghetti" (band diagrams). Connect it to something.