capital of Italy vs national capital

capital of Italy and national capital both are nouns.

Word	Noun	Adjective	Verb	Adverb
capital of Italy	Yes	No	No	No
national capital	Yes	No	No	No

capital of Italy (noun)	national capital (noun)
capital and largest city of Italy; on the Tiber; seat of the Roman Catholic Church; formerly the capital of the Roman Republic and the Roman Empire	the capital city of a nation