Negative thinkers sit in his complex outside Lima (9)
I believe the answer is:
nihilists
'negative thinkers' is the definition.
(people who don't believe in anything)
'sit in his complex outside lima' is the wordplay.
'complex' is an anagram indicator.
'outside' is an insertion indicator.
'lima' becomes 'l' (phonetic alphabet: alpha, bravo, charlie etc.).
'sit'+'in'+'his'='sitinhis'
'sitinhis' is an anagram of 'nihiists'.
'nihiists' going around 'l' is 'NIHILISTS'.
(Other definitions for nihilists that I've seen before include "unbelievers" , "They reject all theories of morality or religious belief" , "Old revolutionaries" .)