Abinitio relativistic molecular orbital self-consistent field calculations for the thorium–platinum diatomic

Abstract

Abinitio relativistic as well as the corresponding non-relativistic limit (NRL) MO calculations are reported for the ground state (Ω = 0) of the closed-shell diatomic ThPt. It is found that relativistic effects lead to a very pronounced bond shortening of ca 1.68 bohr. The predicted bond length of 2.7398 Å with the relativistic molecular orbital (RMO) wavefunction (WF) for the diatomic ThPt is ca. 0.25 Å shorter than the Th—Pt distance reported in a recently synthesized complex with a thorium–platinum bond as well as the shortest Th—Pt bond distance reported for the Th–Pt alloy. The calculated relativistic total molecular energy and the force constant at the predicted bond distance of 5.1774 bohr are −44 963.5050 hartree and 0.34650 hartree/(Å)2, whereas the corresponding predicted non-relativistic values are 6.824 bohr, −41 690.6970 hartree, and 0.08388 hartree/(Å)2, respectively. The vibrational frequencies predicted by the RMO and the non-relativistic limit MO SCF wavefunctions are 155.4 cm−1 and 76.46 cm−1, respectively. The relativistic effects are very pronounced for ThPt and lead to a very significant bond contraction, an almost fourfold increase in the force constant, and doubling of the vibrational frequency. Keywords: relativistic effects, ThPt, RMO, bond contraction, DF SCF.