In cases of problematic open-shell references, e.g., strongly spin-contaminated doublet radicals, one may choose to use DFT orbitals, which can yield significantly improved results.[Beran et al.(2003)Beran, Gwaltney, and Head-Gordon] This can be achieved by first doing DFT calculation and then reading the orbitals and turning the Hartree-Fock procedure off. A more convenient way is just to specify EXCHANGE, e.g., EXCHANGE = B3LYP means that B3LYP orbitals will be computed and used in the CCMAN/CCMAN2 module, as in the following example.
Example 6.95 CCSD calculation of triplet methylene using B3LYP orbitals
$molecule
0 3
C
H 1 CH
H 1 CH 2 HCH
CH = 1.07
HCH = 111.0
$end
$rem
JOBTYPE sp single point
EXCHANGE b3lyp
CORRELATION ccsd
BASIS cc-pvdz
N_FROZEN_CORE 1
$end