You are right, a night train runs between Paris (Austerlitz train station) and Barcelona daily. Departure from Barcelona at 21:05, arriving in Paris at 9:02. Back from the French capital, the trains leave at 20:41, arrive in Barcelona at 8:24. The journey time is approximately 11 hours and 50 minutes Ticket prices and timetable can be found on the official website of the Spanish Railways: www.renfe.com