What is the origin of rotational barrier in ethane?
In most organic chemistry textbooks, we learned that it's originated from steric repulsion between two methyl groups. But recently I heard that there also exists other perspective which explains rotation barrier using hyperconjugation model.
So I searched and read many papers about the origin of rotational barrier in ethane and I notice that there are two competing models for explaining this rotation barrier.
But there are no significant conclusions and it still remains controversy "what is the primary energy term in rotation barrier?". Because many authors suggested many calculations to prove what is mainly contributed to rotation barrier and there results for supporting there argument, but each calculation is based on different approximations and theories. (e.g. NBOs are not optimal --> hyperconjugation energy is overestimated)
So my question is that "Is there no conclusion? What factor mainly contributes to ethane rotation barrier?"