Restoring rotational symmetry of multicomponent wavefunctions with nuclear orbitals

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate multicomponent quantum chemistry calculations are essential for describing systems with light nuclei, such as hydrogen.
• Rotational symmetry is often broken in calculations involving localized nuclear orbitals, necessitating corrections.
• Existing methods struggle to accurately account for rotational effects and proton-electron correlation.

Purpose of the Study:

• To develop and apply a non-orthogonal configuration interaction (NOCI) approach for rotational corrections in multicomponent quantum chemistry.
• To improve the accuracy of proton binding energy predictions in diatomic (HX) and triatomic (HXY) molecules.
• To investigate the performance of NOCI with Hartree-Fock (HF) and density functional theory (DFT) frameworks.

Main Methods:

• Implementation of a non-orthogonal configuration interaction (NOCI) method.
• Application of NOCI to multicomponent calculations using HF and DFT (epc17-2 functional).
• Development of a scaling scheme to correct for double-counting of correlation effects in DFT.

Main Results:

• NOCI significantly improves proton binding energy predictions at the HF level, with average corrections of 0.46 eV (HX) and 0.23 eV (HXY).
• HF kinetic energy corrections are accurate for rotational excitation energies, but total energy predictions are limited by correlation effects.
• Scaled NOCI-DFT results show excellent agreement with CCSD(T) data, with small deviations for rotational transitions (avg. 1.0 cm-1).

Conclusions:

• The NOCI approach effectively restores rotational symmetry and enhances accuracy in multicomponent calculations.
• HF calculations benefit greatly from NOCI rotational corrections, while DFT requires a scaling scheme to address correlation overestimation.
• The proposed scaled NOCI method provides a reliable way to compute accurate proton binding energies and rotational transitions.