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.82 This can be achieved by first doing DFT calculation and then reading the orbitals and turning the SCF procedure off.
Example 6.28 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 EXCHANGE b3lyp BASIS cc-pvdz $end @@@ $molecule read $end $rem BASIS cc-pvdz METHOD ccsd SCF_GUESS read MAX_SCF_CYCLES 0 N_FROZEN_CORE 1 $end