I have three questions around geometry and concave surfaces in chemistry.

This wonderful plant virus

https://www.nature.com/articles/s41467-018-04793-6

is only 18nmx30nm and consists of two fused(!) icosahedra. Hence, there is a tiny concave surface, nearly on the molecular scale, which IMO is very rare, except for the many examples of enzymes, maybe?

--> 1. Are concave surfaces on the nanoscale rare?

Fused icosahedra are very rare in chemistry.

--> 2. Is that true?

See e.g. chart 4 in https://pubs.rsc.org/en/content/articlehtml/2016/cs/c6cs00159a

for the arguably best-known case of B12 icosahedra.

--> 3. Are there more examples?

I thought of pagodanes, https://pubs.acs.org/doi/abs/10.1021/ja00249a029

I am interested in answers that contain proper references to scientific literature (incl. textbooks). I should be grateful if you abstain from the AI rubbish that is increasingly clogging up researchgate!