My first name is "Luca", my last name is "de Alfaro".
If you confuse the two, and write
I will immediately conclude that you don't know me, and I might not read on!
I like to sign papers in alphabetical order. I really do. Signing in alphabetical order makes collaboration much easier and more pleasant, avoiding difficult issues of how exactly to rank the contributions of different authors. Hence, the question of how to alphabetize my last name comes up relatively often.
In Italy, my home country, my last name used to be always alphabetized under 'D'. Moreover, I now have some papers with people whose last names fall between 'Alfaro' and 'de' in the alphabetical order, and I chose to be after them in the list of authors; hence, in the interest of consistency, I prefer to be always alphabetized under 'D'. My father, a physicist, also always alphabetizes our last name under 'D' in research papers.
Ah, now to the fine points. It depends. These are correct ways:
Simple: just write
author = "de Alfaro, Luca"This also works:
author = "L. de Alfaro"