Ground states of the Mo2, W2, and CrMo molecules: A second and third order multireference perturbation theory study

Abstract

The potential energy curves of the molecules Mo(2), W(2), and CrMo have been studied ab initio using large basis sets and the "n-electron valence state perturbation theory" up to the third order in the energy. The third order results for Mo(2) and W(2) reproduce the equilibrium distances r(e) and the harmonic frequencies omega(e) in fairly good accordance with the experimental values but tend to underestimate the dissociation energy. The CrMo molecule, for which experimental dissociation energy data do not exist yet, is predicted to have a value for D(e) of approximately 2.5 eV.

Potential energy curves for Mo2: multi-component symmetry-projected Hartree–Fock and beyond

“…In particular, a minimum near 2.1 Å is predicted in both cases, with a binding energy of ≈13.3 and ≈32.2 mhartree with D ∞h S-UHF and D ∞h KS-UHF, respectively. The shape of the curve is also in good agreement with previously reported accurate PEC profiles [24,25], that is, the minimum is located at a short inter-nuclear separation, with a characteristic non-Morse like behaviour defined by the shallow binding occurring at longer Mo-Mo distances.…”

“…However, a proper description of the dissociated atoms was not achieved due to the shortcomings in their wavefunctions. In a more recent study, Angeli, Cavallini, and Cimiraglia [24] using the multi-reference n-electron valence state perturbation theory and sufficiently large basis sets reported a high-quality PEC for this system in its ground state. Shortly after, Borin, Gobbo, and Roos [25] using multi-configurational self-consistent field (SCF) and second-order perturbation theory reported a high-quality PEC of Mo 2 in the ground state as well.…”

“…The Cr 2 and Mo 2 molecules, containing group VIB transition metal atoms, can be both regarded as containing a formal sextuple bond (see Ref. [16] for more details) and have been excellent targets [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] for testing novel ab initio methods. When estimating the quality of theoretical results, the availability of experimental data [6][7][8][9] for these molecules is very important.…”

“…There have been a number of ab initio studies [17,20,21,[23][24][25]28] of the molybdenum dimer in the ground 1 + g state, most of them focusing on the molecular properties at near-equilibrium geometries. A more stringent task is a correct description of the shape of the PEC at geometries that are far from the equilibrium arrangement [32].…”

A multireference perturbation theory study on the Fe2molecule: in quest of the ground state

“…The perturbation calculations have been done by leaving the 1s, 2s and 2p electrons uncorrelated. In this work we have drawn on the experience gained in our previous studies on the transition metal dimers for the group VI elements [34,39] (Cr 2 , Mo 2 , W 2 and CrMo), for Mn 2 [40] and for Sc 2 [35].…”