Isn't it delightful that NWChem6.6, the just released, and 6.5 can be successfully compiled on the newest MAC OS X EI Capitan 10.11 with GCC 5.2.0 and MPICH2 3.1.4_1?
The compilation of the just released NWChem6.6, with MRCC methods enabled, has been successful on MAC OS EI Capitan 10.11.1 having Xcode 7.1, GCC 5.2.0 and MPICH2 3.1.4_1 installed.