what is the conceptual framework of gothic literature

The conceptual framework for the Gothic is the unconscious. The Gothic deals with the hidden, the supernatural, the frightening, the horrible, and the bizarre: all the parts of life we repress. Three psychological terms often associated with the Gothic are "unheimlich," "uncanny," and "doppelgänger."
What is unheimlich is unhomelike: strange, bizarre, and creepy. We tend to connect the Gothic with strange, often frightening settings: medieval castles, darkness, fog, swamps, isolated places, dungeons, and cellars.
The uncanny is unsettling or mysterious, both like and yet creepily not like the ordinary and everyday. Freud said that the corpse is the figure of the uncanny: it is both wholly human and wholly inhuman. It confronts us with what we don't want to face, our own mortality. Other uncanny objects are the backs of ourselves, as we don't usually see that aspect of our being—it can be startling, for example, to see a picture of our backs. Dolls are also emblems of the uncanny because they look human and yet aren't. Corpses and creepy dolls often play a role in Gothic literature.
The word doppelgänger means twin, and often Gothic literature features twinning, even if it is simply a person seeing their own face in the mirror in a startling way. The twin is often the reflection of ourselves that shows us something we don't want to see or ordinarily wouldn't see. An example of an eery twin is Roderick's twin sister Madeline in "The Fall of the House of Usher." She actually seems to be a corpse and then to come to life.
Essentially, the Gothic puts us in touch with those parts of ourselves and our world that the rational mind wants to exclude or the psyche wants to repress. Gothic literature is often understood as a response against the rationalism of the Enlightenment, a way to explore the unconscious mind and/or that which frightens and repels us.