Idea of negative charge (6)
I believe the answer is:
notion
'idea' is the definition.
(notion is a kind of idea)
'negative charge' is the wordplay.
'negative' becomes 'not' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'charge' becomes 'ion' (an ion is a charged particle).
'not'+'ion'='NOTION'
'of' is the link.
Can you help me to learn more?
(Other definitions for notion that I've seen before include "Vague understanding" , "Whim or fancy" , "Vague or fanciful idea" , "Idea or whim" , "Idea or fancy" .)