Real or artifactual symmetry breaking in the BNB radical: A multireference coupled cluster viewpoint

Abstract

The ground state of the linear BNB radical has been examined via the recently developed reduced multireference coupled cluster method with singles and doubles that is perturbatively corrected for triples [RMR CCSD(T)] using the correlation consistent basis sets (cc-pVXZ, X=D, T, and Q). Similar to earlier results that were based on the single reference CCSD(T) and BD(T) approaches, the RMR CCSD(T) method also predicts an asymmetric structure with two BN bonds of unequal length, even though the MR effects significantly reduce the barrier height. The computed frequencies for the symmetric and antisymmetric stretching modes agree reasonably well with the experimental data.

Multireference Coupled-Cluster Methods: Recent Developments

“…At the SR-level, it has been especially the RMR CCSD approach [118,121,206] and its truncated [205] and RMR CCSD(T) [203] versions that proved to be very useful in actual applications, enabling us to handle even rather strong quasi-degeneracies and thus providing an accurate treatment of a number of both important and challenging systems, including open-shells [121]. Indeed, these methods turned out to be very efficient not only in generating of entire potential energy surfaces or curves for small species [119,[214][215][216] (e.g., HF, F 2 , H 2 O, LiH, BN, C 2 , BNB, N 3 , etc. ), including a very demanding case of the triple-bond breaking in the nitrogen molecule [176,217] (see also [122]), but also enabled the handling of relatively large systems, such as nickel-carbonyls [218] and transition metal ion -methylene complexes [219].…”

Symmetry-breaking in the independent particle model: nature of the singular behavior of Hartree–Fock potentials

“…The general nature of PESs or PECs of the kind arising in the presence of a spinpreserving symmetry breaking has been briefly pointed out earlier [4,5,9,17] but, due to the above explained difficulties, these potentials have never been explicitly generated in full detail. In the closed-shell case the general form of this type of a singular behavior was described by Mestechkin (see Fig.…”

“…This is indeed the case in many instances, at least when investigating standard molecular systems in the vicinity of their equilibrium geometry. However, when considering entire potential energy surfaces (PESs) or curves (PECs), even for atoms and diatomics, this is no longer the case (see, e.g., [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]; for reviews see [18][19][20][21]). Yet, the fact that E[Φ 0 ] represents a stationary point on E[Φ] is no guarantee that it represents the absolute minimum or, in fact, even a local minimum.…”

“…In such cases the instability and the corresponding BS solutions may disappear when the correlation effects are properly accounted for and a complete basis set limit is approached (cf., e.g., [38]). Even when the symmetry breaking persists at the correlated level, this effect may be extremely small to be verified experimentally (cf., e.g., the results for the BNB and N 3 species [9,11]). Nonetheless, even though the symmetry breaking may not appear at the equilibrium geometry, it will manifest itself sooner or later away from the equilibrium.…”

Non-covalent attraction of B2N(−,0) and repulsion of B2N(+) in the B n N n ring: a quantum rotatory due to an external field

“…A number of experimental as well as theoretical studies have been devoted to this system [1][2][3][4][5][6][7][8][9][10][11][12]; however, there are no reports on the SB of ionic structures in a non-covalent interaction with B n N n rings (except for a brief study in our previous works) [13][14][15][16].…”