Get the tourist visa. And be sure to do a bit of sightseeing.

You are making a mountain out of a molehill. I am sure getting the appropriate visa should not be a problem.

Are you not able to visit the embassy and find all the facts?
Are you not able to get advice from your institution that is sending you to the conference?
Do you not have a travel agent who may be able to share some tips since others from India also go to scientific conferences.

Asking people of Fodors is helpful, yet they do not really know the rules that may strictly apply to the two countries and to a student attending a scientific conference.

I am just trying to give you options to look into, so you can get your visa in time.

Have fun planning and then enjoy a safe trip.

Get a tourist/visit visa.
You are not doing paid work whilst in Germany. You undoubtedly will do some sightseeing while in Germany. Make sure you present all the documentation required for the visit. If they interview you say you are going for a short visit. No need to mention the conference at all.

Update: Applying for a visit visa with purpose as: Scientific Conference. Let's see what happens.
And all you guys: Thanks a frikkin lot. You have been of great help to me over last one month. Cheers :)