capital of Thailand vs national capital

capital of Thailand and national capital both are nouns.

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

capital of Thailand (noun)	national capital (noun)
the capital and largest city and chief port of Thailand; a leading city in southeastern Asia; noted for Buddhist architecture	the capital city of a nation