Theories about efficient market/exchange is _liberalism_. Capitalism is an ideology about who own the means of production: in this case, the person who own the capital. When the state OR a "commune" owns the mean of production, this is communism. But you can definitively have a "free market communism", except WTO will probably disagree on whether product issued by a state controlled industry really respect its rules.

You can also the two, like in the nordic countries (or germany) where employee actually have voting power about the strtegic orientation of the company (actually i think employees are considered "owning" 30% of the issued shares or something like that). From a (weird) point of view, this is 70% capitalism, 30% communism.