Improved theoretical calculations of InN in its X3Σ− ground state and in the first 3Π excited state

Spectroscopic constants of the two lowest states of the InN molecule, the X3Σ− ground and the 3Π excited state were calculated using the restricted open-shell Hartree–Fock Coupled Cluster ROHF-CCSD(T) method with single, double and perturbative triples, the complete active space second-order perturbation theory (CASPT2) and the multireference configuration interaction (MRDCI) methods. Relativistic pseudopotentials (for MRDCI) and atomic natural orbital basis set for treating spin–orbit and scalar relativistic effects – ANO-RCC (for CCSD(T), CASPT2 and CASPT2/RASSI-SO) were used. The accuracy of different methods was compared correlating up to 26 valence and core-valence electrons of N and In atoms.