Drop D tuning
From Riff Wiki
Tune the low E down a whole step to D. Power chords become one-finger barres across the bottom three strings; the open low string gives you a heavy D.
D|-0-0-3-3-5-5-0-0-| A|-0-0-3-3-5-5-0-0-| D|-0-0-3-3-5-5-0-0-|
Watch intonation on cheap guitars; the loose string may buzz. Use a slightly heavier low string if you live in drop D.