Apply German residence permit in UK?

Hi, I will have an academic visit to the MPII in Germany for 6 months. Which visa (Shengen visa or residence permit) I should apply? I personally think I have to apply residence permit, as the Shengen visa allows the holder to travel as a tourist for periods up to 90 days per six months.

If I have to apply residence permit, I am not sure if I have to apply in London, or in Edinburgh (I am living in Durham, UK). The website in Edinburgh doesn't mention too much on how to apply residence permit, and moreover, after booking the appointment in Edinburgh, I got a confirmation letter, saying your appointment for applying for a Shengen visa (NOT residence permit) has been successful.

I know the applicants who are living in Durham should apply a Shengen visa in Edinburgh (NOT in London). I am wondering if this also applies to the application of residence permit.

A category D visum may be possible too and can be valid for up to 12 months. Best to directly contact the German embassy.