document: The optimised structure at the B3LYP/aug-cc-pVTZ level was then used to perform calculations of the lowest electronic singlet excited states with the coupled cluster linear response (LR) coupled cluster hierarchy CCS, CC2, CCSD and CC3, along with perturbative corrected methods CIS(D) and CCSDR(3). The correlated response methods were performed with an all-electron atomic natural orbital (ANO) basis set contracted to 6s5p4d3f1g on manganese, [47] together with the cc-pVTZ basis set on the oxygen atoms. The all-electron correlated calculations invoked a 13 orbital frozen core (O 1s, Mn 1s2s2p3s3p). Trial calculations correlating these orbitals only had a minor effect on excitation energies. For comparison the EOM-CCSD method with the cc-pVTZ basis on all atoms was tested to compare with LR-CCSD. These formally give exactly the same excitation energies, although the transition moments are more accurate for LR-CCSD. Abelian symmetry (D2) was used in all correlated excited state calculations.
extractive_keyphrases: 6s5p4d3f1g abelian symmetry ano atomic natural orbital cc2 cc3 ccs ccsd correlated response methods coupled cluster hierarchy d2 excitation energies excited state calculations linear response lowest electronic singlet lr manganese mn o optimised structure oxygen perturbative corrected methods transition moments
abstractive_keyphrases: all-electron correlated calculations b3lyp/aug-cc-pvtz cc-pvtz ccsdr(3) cis(d) eom-ccsd method lr-ccsd