A study of the ground state of manganese dimer using quasidegenerate perturbation theory

Abstract

We study the electronic structure of the ground state of the manganese dimer using the state-averaged complete active space self-consistent field method, followed by second-order quasidegenerate perturbation theory. Overall potential energy curves are calculated for the 1Sigmag+, 11Sigmau+, and 11Piu states, which are candidates for the ground state. Of these states, the 1Sigmag+ state has the lowest energy and we therefore identify it as the ground state. We find values of 3.29 A, 0.14 eV, and 53.46 cm(-1) for the bond length, dissociation energy, and vibrational frequency, in good agreement with the observed values of 3.4 A, 0.1 eV, and 68.1 cm(-1) in rare-gas matrices. These values show that the manganese dimer is a van der Waals molecule with antiferromagnetic coupling.

Density functional study of manganese dimer

“…We only examine BLYP and B3LYP calculations of all spin states with a larger basis set ([18s15p8d4f2g/7s6p4d4f2g]) employed in Ref. 33. Then we found that the deviations from the data shown below on binding energies and equilibrium distances, are within 0.02 eV and 0.02 Å, respectively, and confirmed that all features of potential surfaces, such as relative stabilities and humps are unchanged.…”

“…Some researchers using KS-DFT pointed out, the experimentally reported spectroscopic constants and/or singlet stability of Mn dimer are observed not in the gas phase, but in the rare gas matrix, so that it is possible to deviate the observed state from that of ab initio results. However, Wang and Chen [32], and Yamamoto et al [33]. have recently showed that multireference perturbation theory (MRMP2) calculations yield spectroscopic constants of the potential surface of Mn 2 , which are similar to those of experimentally reported values.…”

“…These KS-DFT and hybrid DFT results are classified in the three tables for "leading" exchange terms, Becke88/Slater or X␣/GGA, PBE, or meta-GGA (TPSS), respectively. Experimental [36 -39] and MRMP2 results [33] are also listed for comparison.…”

“…The fact that the 1 g ϩ state is not bound at the complete-active-space self-consistent field (CASSCF) level [32][33][34] with including 3d and 4s orbitals-andelectrons in the active-space, but the CASSCF followed by second-order perturbation theory yields the correct spectroscopic constants [32,33], suggests that both of the static and dynamic correlation effects are essential for description of chemical bonding of Mn 2 . Although this type of explicit quantum many-body (MR and/or PT) approaches are straightforward and reliable ways in the context of quantum mechanics for molecular systems [45], they are computationally impracticable for applications to large metal clusters.…”

“…In addition, the counterpoise method is employed to remove basis set superposition error [65]. The zero-point correction is also considered to compute the spectroscopic constants, but the relativistic effects are ignored since the spin-orbit interaction, the leading term of the relativistic correction, is reported not to affect the computational results [33].…”