Does Divine Smite works with Unarmed Attacks and/or Natural Weapons?

On a related note, myself and a large group online have been trying to figure out whether Divine Smite works with Unarmed Attacks and/or Natural Weapons. It seems like you’ve both said it does and does not work. Would you be willing to help us out by clarifying?

Are the 9 hells and layers of the abyss round planets?

Is spellcasting not an ability?

The idea of a ‘group check’ is in the rules anywhere in 5e, or is your homebrew rule?

Why Forge cleric does not gain martial weapon proficiency, but is able to use Blessing of the Forge on a martial weapon?

Druid’s Wild Shape, it says you “retain any abilities given by your class/race” : could I still use psionic powers?