I am not a subject expert here at all so I don’t know if I understand exactly what you mean by “methods that would let you design such a thing in-silico”, but there was a paper[0] and interview with its authors[1] published a year ago about a drug-development AI being used to design chemical weapons.

[0] https://www.nature.com/articles/s42256-022-00465-9

[1] https://www.theverge.com/2022/3/17/22983197/ai-new-possible-...