# 5.11 Non-Hartree-Fock Orbitals in Correlated Calculations

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 [279]. 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.

## 5.11.1 Example

**Example 5.101** 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