Theoretical study on low-lying electronic states of NiH2

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Physics

Background:

• Understanding the electronic structure of transition metal compounds like NiH2 is crucial.
• Accurate theoretical models are needed to describe electron correlation in such systems.

Purpose of the Study:

• To investigate the low-lying electronic states of the NiH2 molecule.
• To accurately describe strong electron correlation from the nickel 3d9 super-configuration.
• To compare theoretical findings with experimental observations.

Main Methods:

• Multi-Configuration Quasidegenerate Perturbation Theory (MCQDPT2) method.
• Inclusion of diffuse secondary 3d' orbitals in the active space (12 electrons in 13 orbitals).
• Comparison with other single- and multi-configurational methods.

Main Results:

• The minimum energy configuration of NiH2 is bent, aligning with experimental data.
• The global ground state is identified as 1A1 (or A1 with spin-orbit coupling).
• The lowest linear state is determined to be 3Deltag (or 3g).

Conclusions:

• The MCQDPT2 method with an extended active space accurately describes NiH2 electronic states.
• Theoretical findings suggest potential inaccuracies in the experimental frequencies of NiH2 and NiD2.
• The study highlights the limitations of simpler computational methods for this system.