Although drop D is the obvious clue and the simple single finger power bar chords, the actual harmony is just a series of stacked perfect 4ths (possible Root, perfect 4th and flattened 7th) This could even be interpreted in a very modern 'out there' jazz style in the style of Mccoy Tyner. (John Coltrane's piano player). I love these chords.. I find their inherent instability and dissonance very satisfying.
Played at the 5th fret any of these could be the chord name:
A7sus4 | A 7th Suspended 4th |
Dsus4/A | D/A Suspended 4th |
Gsus2/A | G/A Suspended 2nd |