Is there a list which provides the nations that could, without either external expertise or external materials (say from current domestic inventory of nuclear energy industry), develop a nuclear weapon?
This isn't the kind of thing that people list publicly. It would stand as a challenge to countries that are not on the list and serve as encouragement to those on the list. The closest official list would be the list of forty-eight countries in the Nuclear Suppliers Groups (NSG). The NSG is a list of countries that are officially approved to trade in nuclear materials, selling them to other countries. However, that list has some obvious omissions for this purpose.
In particular, the two candidate countries, India and Pakistan, already have nuclear weapons but aren't yet in the NSG. North Korea and Iran aren't on that list, but North Korea already has nuclear weapons and Iran should be considered a risk. Israel probably has nuclear weapons but is not in the NSG.
It's also worth noting that countries that have developed nuclear weapons in the past have generally had help from other countries. In some cases, they stole that help through espionage.
The United States had help from the United Kingdom and Canada in its Manhattan Project. This also included support from German citizens like Albert Einstein and Rudolf Peierls (who lived in the UK after the beginning of World War II) and French citizens like Bertrand Goldschmidt. The UK and France thus were also helped by the US and each other.
The Soviet Union took some of the German scientists after the war and was engaged in active espionage against the Allies.
China had help from the Soviet Union in their program.
Israel was helped by Jewish scientists around the world, possibly including some who worked on the Manhattan Project.
India was still part of the British empire at the end of World War II and bought some nuclear technology from the Soviet Union.
Pakistan bought technology from China and engaged in espionage to develop nuclear weapons.
North Korea had help from Pakistan and possibly China and Russia.
Iran has had help from Russia.
Perhaps there are countries that could develop nuclear weapons alone. But in practice, that's not the way that any did it.
Any sufficiently industrialized nation can develop nuclear weapons nowadays, especially if they invest vast amounts of money into it.
The principles behind nuclear fission and nuclear fusion are well understood by now all around the world and thus it is mostly a question of gaining access to raw materials and money to develop and run a nuclear weapons program.
I'd dare say that all of the G20 states could - if they are not already doing it or have done it - develop a fission weapon in 12-24 months and a fusion weapon in another 24-36 months if they really wanted to.
Even North Korea could develop fusion weapons. So except for some micro nations and some really really poor nations or failed states probably everyone could create nuclear weapons - albeit at the cost of their own population starving etc.