capital of Portugal vs national capital

capital of Portugal and national capital both are nouns.

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

capital of Portugal (noun)	national capital (noun)
capital and largest city and economic and cultural center of Portugal; a major port in western Portugal on Tagus River where it broadens and empties into the Atlantic	the capital city of a nation