Ab initio calculations for the potential curves and spin-orbit coupling of Mg 2

Abstract

The ground state and several low-lying excited states of the Mg 2 dimer have been studied by means of a combination of the complete-active-space multicon®gu-ration self-consistent-®eld (CASSCF)/CAS multireference second-order perturbation theory (CASPT2) method and coupled-cluster with single and double excitations and perturbative contribution of connected triple excitations [CCSD(T)] scheme. Reasonably good agreement with experiment has been obtained for the CCSD(T) ground-state potential curve but the dissociation energy of the only experimentally known A 1 R u excited state of Mg 2 is somewhat overestimated at the CASSCF/CASPT2 level. The spectroscopic constants D e , R e and x e deduced from the calculated potential curves for other states are also reported. In addition, some spin±orbit matrix elements between the excited singlet and triplet states of Mg 2 have been evaluated as a function of internuclear separation.

Scattering length of the ground-stateMg+Mgcollision

“…For example, the induced dipole-dipole dispersion coefficient of Ref. [30] is about a factor of 2 larger, while that of our MVB calculation is about 15% smaller, than that of Ref. [37].…”

“…This paper briefly describes our ab initio multiconfiguration valence bond (MVB) calculation of the ground state potential. Although, as we will show, the theoretical uncertainty in the shape of the potential is too large to predict the scattering length we nevertheless compare scattering data for our ab initio potential and the most recently published theoretical potential by Czuchaj et al [30] to those for the RKR and IPA potential. This will give us a feeling for the state of the art in molecular electronic structure calculations of interacting two electron atoms.…”

“…The question becomes how well a computational approach can incorporate these correlations. There are a large number of methods [19][20][21][22][23][24][25][26][27][28][29][30] which have been tested for the computation of the correlation corrections. In a pioneering publication Stevens and Krauss [23] calculated the ground state potential of Mg 2 using a nonrelativistic multiconfiguration self-consistent field method.…”

“…[30] a combination of a coupled-cluster method with single and double excitations and perturbative triple excitations is used to reach a good agreement with the RKR potential of Ref. [17].…”

“…[17] and improved upon the RKR analyses by applying a variational procedure based on the inverted perturbation approach (IPA). Finally, there exist a large number of theoretical electronic structure calculations [19][20][21][22][23][24][25][26][27][28][29][30] of the ground state Mg 2 potential. This paper briefly describes our ab initio multiconfiguration valence bond (MVB) calculation of the ground state potential.…”