Components of the Bond Energy in Polar Diatomic Molecules, Radicals, and Ions Formed by Group-1 and Group-2 Metal Atoms

Abstract

Although many transition metal complexes are known to have high multireference character, the multireference character of main-group closed-shell singlet diatomic molecules like BeF, CaO, and MgO has been less studied. However, many group-1 and group-2 diatomic molecules do have multireference character, and they provide informative systems for studying multireference character because they are simpler than transition metal compounds. The goal of the present work is to understand these multireference systems better so that, ultimately, we can apply what we learn to more complicated multireference systems and to the design of new exchange-correlation functionals for treating multireference systems more adequately. Fourteen main-group diatomic molecules and one triatomic molecule (including radicals, cations, and anions, as well as neutral closed-shell species) have been studied for this article. Eight of these molecules contain a group-1 element, and six contain a group-2 element. Seven of these molecules are multireference systems, and eight of them are single-reference systems. Fifty-three exchange-correlation functionals of 11 types [local spin-density approximation (LSDA), generalized gradient approximation (GGA), nonseparable gradient approximation (NGA), global-hybrid GGA, meta-GGA, meta-NGA, global-hybrid meta GGA, range-separated hybrid GGA, range-separated hybrid meta-GGA, range-separated hybrid meta-NGA, and DFT augmented with molecular mechanics damped dispersion (DFT-D)] and the Hartree-Fock method have been applied to calculate the bond distance, bond dissociation energy (BDE), and dipole moment of these molecules. All of the calculations are converged to a stable solution by allowing the symmetry of the Slater determinant to be broken. A reliable functional should not only predict an accurate BDE but also predict accurate components of the BDE, so each bond dissociation energy has been decomposed into ionization potential (IP) of the electropositive element, electron affinity of the electronegative bonding partner (EA), atomic excitation energy (EE) to prepare the valence states of the interacting partners, and interaction energy (IE) of the valence-prepared states. Adding Hartree-Fock exchange helps to obtain better results for atomic excitation energy, and this leads to improvements in getting the right answer for the right reason. The following functionals are singled out for reasonably good performance on all three of bond distance, BDE, and dipole moment: B97-1, B97-3, MPW1B95, M05, M06, M06-2X, M08-SO, N12-SX, O3LYP, TPSS, τ-HCTHhyb, and GAM; all but two (TPSS and GAM) of these functionals are hybrid functionals.

Information on Gas‐Phase Diatomic Molecules from Magnetically Induced Current Densities

“…For instance, Truhlar and Yu showed that CaO, MgO, and MgS, despite being in a singlet state, have multireference character. [50] Similarly, Badri et al have reviewed the ring current model in all-metal clusters and they found that in the Sc 2 3 cluster a multireference study is necessary. [51] Conversely, the MICD module in DIRAC is not programmed to treat multireference ground states and, therefore, the present study utilized the same approach as for the other molecules.…”

A look at the density functional theory zoo with the advanced GMTKN55 database for general main group thermochemistry, kinetics and noncovalent interactions

“…23 However, closer analysis shows that ''pure'' one-electron SIEeffects are hard to capture with this set, and therefore we herein ) for which their dissociation energies at four different points along their dissociation potential energy curves are calculated: at their respective inter-monomeric equilibrium distance, 1.25 times, 1.5 times and 1.75 times their equilibrium distance. The relevant structures were optimised at the SCS-MP2 117 /def2-TZVPP level 59 We adopted ten of those dimers from their study to form the new ALKBDE10 test set: BeF, BeO, CaO, HF, KF, LiF, KF, LiF, LiO, MgO, MgS, and NaO. All structures are based on the PW6B95-D3(BJ)/def2-QZVPP level of theory.…”

ACCDB: A collection of chemistry databases for broad computational purposes

“…For more details of all the subsets of every database, as well as references to their original sources, and a better overview of their overlaps, see also the Supporting Information …”