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ATAT calls the gnuplot module in some of its commands behind the scenes and requires the creation of the .gnuplot file in the users home directory as detailed on the gnuplot wiki page.
VASP Interface
ATAT has the ability to interface with VASP which requires the user to have access to an install of VASP. For more details about setting up the interface please refer to the link: https://www.brown.edu/Departments/Engineering/Labs/avdw/atat/manual/node11.html