Many-body perturbation theoretic calculation of the nuclear spin-coupling constant in the hydrogen molecule

Abstract

The Fermi contact term of the nuclear spin-coupling constant in the HD molecule is calculated by diagrammatic many-body perturbation theory (MBPT) employing extended Gaussian basis sets in the standard Hartree–Fock potential. The calculation through second order in electron correlation gives a value for the coupling constant of 28.1 Hz, which is only 65% of the experimental value. However, Hartree–Fock exclusion principle violating diagrams are found to contribute significantly. By summing these dominant diagrams selectively by the geometric approximation, we obtain a value of 37.0 Hz. The convergence is enhanced with shifted denominators, which finally yield 38.0 Hz within ∼10% of the probable Fermi contact value. Advantages of MBPT in calculating nuclear spin-coupling constants are discussed.