Wrote music that's calm (8)
I believe the answer is:
composed
This clue is a double definition.
'wrote music' is the first definition.
('compose' can be a synonym of 'write music')
'calm' is the second definition.
('composed' can be similar in meaning to 'calm')
'that's' is the link.
(Other definitions for composed that I've seen before include "cool" , "Field did" , "What poet did" , "What Gershwin did" , "with aplomb" .)