In the spin-coupled generalized valence bond (SCGVB) description of Be2, there is a pair of electrons in highly overlapping “inner” orbitals corresponding to a traditional σ bond, but this bond is compromised by Pauli repulsion arising from its overlap with a second “outer” pair. The presence of this outer pair of electrons leads to a repulsive potential energy curve at long range and a bound, but metastable molecule at short range. To obtain further insights into the nature of the bond in Be2, we determined the non-dynamical and dynamical correlation contributions to the potential energy curve of Be2 using four different choices for the zero-order wave function: Restricted Hartree–Fock (RHF), SCGVB, valence-CASSCF(4,4), and valence-CASSCF(4,8). The SCGVB and valence-CASSCF(4,4) wave functions yield similar breakdowns of the total correlation energy, with non-dynamical correlation being the more important contribution. For the RHF and valence-CASSCF(4,8) wave functions, dynamical correlation is critical, without which the potential energy curve is purely repulsive. High accuracy calculations on the HBen−1Be–BeBen−1H molecule as a function of n (n = 1–6) suggest that the intrinsic strength of a Be–Be σ bond uncompromised by Pauli repulsion is on the order of 62–63 kcal/mol, and its length is 2.13–2.14 Å, ∼60 kcal/mol stronger and ∼0.35 Å shorter than in Be2.
Xu, Lu. T. and Dunning, Jr., Thom H.. "The nature of the chemical bond and the role of non-dynamical and dynamical correlation in Be2." Journal of Chemical Physics, vol. 152, no. 21, Jun. 2020. https://doi.org/10.1063/5.0010068
Xu, Lu. T., & Dunning, Jr., Thom H. (2020). The nature of the chemical bond and the role of non-dynamical and dynamical correlation in Be2. Journal of Chemical Physics, 152(21). https://doi.org/10.1063/5.0010068
Xu, Lu. T., and Dunning, Jr., Thom H., "The nature of the chemical bond and the role of non-dynamical and dynamical correlation in Be2," Journal of Chemical Physics 152, no. 21 (2020), https://doi.org/10.1063/5.0010068
@article{osti_1631882,
author = {Xu, Lu. T. and Dunning, Jr., Thom H.},
title = {The nature of the chemical bond and the role of non-dynamical and dynamical correlation in Be2},
annote = {In the spin-coupled generalized valence bond (SCGVB) description of Be2, there is a pair of electrons in highly overlapping “inner” orbitals corresponding to a traditional σ bond, but this bond is compromised by Pauli repulsion arising from its overlap with a second “outer” pair. The presence of this outer pair of electrons leads to a repulsive potential energy curve at long range and a bound, but metastable molecule at short range. To obtain further insights into the nature of the bond in Be2, we determined the non-dynamical and dynamical correlation contributions to the potential energy curve of Be2 using four different choices for the zero-order wave function: Restricted Hartree–Fock (RHF), SCGVB, valence-CASSCF(4,4), and valence-CASSCF(4,8). The SCGVB and valence-CASSCF(4,4) wave functions yield similar breakdowns of the total correlation energy, with non-dynamical correlation being the more important contribution. For the RHF and valence-CASSCF(4,8) wave functions, dynamical correlation is critical, without which the potential energy curve is purely repulsive. High accuracy calculations on the HBen−1Be–BeBen−1H molecule as a function of n (n = 1–6) suggest that the intrinsic strength of a Be–Be σ bond uncompromised by Pauli repulsion is on the order of 62–63 kcal/mol, and its length is 2.13–2.14 Å, ∼60 kcal/mol stronger and ∼0.35 Å shorter than in Be2.},
doi = {10.1063/5.0010068},
url = {https://www.osti.gov/biblio/1631882},
journal = {Journal of Chemical Physics},
issn = {ISSN 0021-9606},
number = {21},
volume = {152},
place = {United States},
publisher = {American Institute of Physics},
year = {2020},
month = {06}}