Krung Thep vs national capital

Krung Thep and national capital both are nouns.

Word	Noun	Adjective	Verb	Adverb
Krung Thep	Yes	No	No	No
national capital	Yes	No	No	No

Krung Thep (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