How do I sign my papers?
In principle, you can use any professional name you like to sign your papers.  I have a few colleagues whose nom de plume (or perhaps nom de LaTeX?) is not the same as their legal name.

But by default, I would recommend signing your papers precisely as you sign anything else, including spaces and accents:


  Jorge Fernández de Cossío Díaz


It would be helpful for people citing your papers to state, somewhere in your CV and on your professional web page, that your last name contains three spaces.  And you'll have to correct copy-editors who incessantly abbreviate it as "J. F. C. Díaz", but you'd have to do that with the other suggested variants anyway.   Modern search engines have no trouble with accents.