Relativistic calculations of dissociation energies and related properties

Abstract

Methods of calculation of potential energy curves or surfaces, including dissociation energies, bond distances, and vibration frequencies, are discussed as well as recently obtained results for several molecules. The ab initio relativistic methods involve the derivation of “shape‐consistent” effective potentials from Dirac–Fock atomic calculations. These effective potentials are averaged and differenced with respect to spin with the differences, p3/2 – p1/2, etc., yielding spin‐orbit operators. The molecular calculations are then set up in a familiar manner through the SCF stage using spin‐averaged effective potentials. The final stage is a configuration‐interaction calculation including the spin‐orbit terms as well as the electron repulsion terms. Calculations that have been made for several low‐lying excited states as well as the ground state for Au2, TlH, Tl2, Sn2, and Pb2 are reviewed. Good agreement is obtained with spectroscopic data and a number of interesting predictions are made.

Comparative study of spectroscopic properties of some indium, tin and antimony compounds

“…For Sn2, Andzelm et al [61] obtained excellent agreement both with experimental and our results for bond length and vibrational frequency using model potentials and local exchangecorrelation spin density functionals (LSD), but the dissociation energy is overestimated by 1 eV as usual with exchange-correlation LSD. Relativistic effective potentials are used by Balasubramanian and Pitzer [62][63][64]; the results show similar deviations to experimental values as ours. R e and ~o e are overestimated by ~0.1 a.u.…”

“…Due to the computational effort and difficulties to describe relativistic effects correctly, mostly pseudopotential or X, results have been published [58][59][60][61][62][63][64][65][66][67][68][69][70][71]. Only for SnH [68], ab initio all-electron calculations have been performed.…”

“…Only for SnH [68], ab initio all-electron calculations have been performed. To our knowledge, papers have appeared on In 2 [58], InH [59], InO [60], Sn2 [61][62][63][64][65], SnH [66][67][68], SnO [69,70], and SbH [71]. For fluorides XF and sulphides XS (X = In, Sn, Sb), no theoretical investigations exist.…”

The zero-order regular approximation for relativistic effects: The effect of spin–orbit coupling in closed shell molecules

“…The molecular D e values, given in Table VI, will be discussed below, but first the molecular spin-orbit effects will be discussed with the help of Tables III-V. In the literature many discussions exist rationalizing spin-orbit effects, especially in the context of ab initio calculations using relativistic effective core potentials ͑ECP͒, see, e.g., the reviews of Pitzer 25 and Ermler et al 26 In particular spin-orbit interaction was analyzed in terms of the bonding between the spin-orbit split ͑j j coupled͒ atomic spinors as a starting point. Here we will use the scalar relativistic approximation as our starting point and we will discuss how the molecular orbitals are modified by the presence of the spin-orbit interaction.…”

Accuracy of relativistic energy-consistent pseudopotentials for superheavy elements 111–118: Molecular calibration calculations

“…For many problems of chemical interest the use of pseudopotentials (PPs) is a sufficiently accurate and efficient approximation, which reduces the number of explicitly treated electrons and includes relativistic effects in a formally nonrelativistic computational framework. [5][6][7][8][9] In a recent paper 10 we presented relativistic energy-consistent PPs for the superheavy elements 111-118 including besides finite nucleus and Dirac relativistic effects also the Breit contribution to electron interaction as well as low-order quantum electrodynamic (QED) effects, i.e., electron self-energy and vacuum polarization. Aside from the computational savings brought about by PPs the easy implicit inclusion of, e.g., the Breit interaction and QED contributions in molecular calculations might for some questions be an advantage over standard relativistic AE calculations which either explicitly use or model merely the Dirac-Coulomb (DC) Hamiltonian.…”