Vulcan is probably not supported on your card
GeForce 600 Series: GeForce GTX 690, GeForce GTX 680, GeForce GTX 670, GeForce GTX 660 Ti, GeForce GTX 660, GeForce GTX 650 Ti BOOST, GeForce GTX 650 Ti, GeForce GTX 650, GeForce GTX 645, GeForce GT 645, GeForce GT 640, GeForce GT 635, GeForce GT 630
according to the dev post it's not supported