Ab initio composite strategies and multireference approaches for lanthanide sulfides and selenides

Abstract

The f-block ab initio correlation consistent composite approach was used to predict the dissociation energies of lanthanide sulfides and selenides. Geometry optimizations were carried out using density functional theory and coupled cluster singles, doubles, and perturbative triples with one- and two-component Hamiltonians. For the two-component calculations, relativistic effects were accounted for by utilizing a third-order Douglas–Kroll–Hess Hamiltonian. Spin–orbit coupling was addressed with the Breit–Pauli Hamiltonian within a multireference configuration interaction approach. The state averaged complete active space self-consistent field wavefunctions obtained for the spin–orbit coupling energies were used to assign the ground states of diatomics, and several diagnostics were used to ascertain the multireference character of the molecules.

Route to Chemical Accuracy for Computational Uranium Thermochemistry

“…High-accuracy model chemistries for molecules containing first- and second-row elements have employed perturbative calculations of scalar-relativistic effects using the Breit-Pauli Hamiltonian with electron-correlation methods and first-order spin–orbit corrections for degenerate open-shell atomic and molecular species. Calculations of molecules containing heavier elements have typically used an additivity strategy augmenting extensive scalar-relativistic electron-correlation calculations with spin–orbit corrections. − This has produced promising results for thermochemical parameters of many heavy-element-containing molecules, including molecules containing early actinide elements. ,,,− …”

Multireference Wavefunction-Based Investigation of the Ground and Excited States of LrF and LrO

“…It is important to note that singlet ground states, especially Σ, are easier to describe with single reference wavefunction methods than higher angular momentum states, particularly for DFT. Though, as shown in prior studies on actinides and lanthanides, density functional methods can result in a broad range of performance for singlet states, with mean unsigned errors (MUEs) from experiment differing by over 15 kcal mol –1 , depending upon functional chosen. ,, As well, for DFT, the “best” functional is not consistent across actinide or lanthanide and ligand, and results can vary significantly. Here, however, the B3LYP/QZ BDE of LrF differs by only ∼0.004 kcal mol –1 from the f -ccCA BDE, which is quite remarkable, considering B3LYP performance in prior studies.…”

“…For the DFT calculations, the DKH3 Hamiltonian with the FC-val electron space was used; these calculations utilized the double-, triple- and quadruple-ζ DK3 basis set. Finally, the f -ccCA scheme was also used as it has been proven to be a viable approach for lanthanide diatomics. , The details of the f -ccCA scheme used are given in the Supporting Information (SI) and described using eqs S1–S5.…”

“…A frequency calculation was then carried out to ensure the minimum on the potential energy curve. The dissociation energy of LrF and LrO were calculated using a composite approach: the f -correlation consistent composite approach ( f -ccCA), , UCCSD­(T), and four different density functionals: the Tao, Perdew, Staroverov, Scuseria (TPSS), the Minnesota 2006 local functional (M06-L), Perdew–Burke–Ernzerhof (PBE), and the Becke, 3-parameter, Lee–Yang–Parr (B3LYP) , functional. These functionals represent three exchange-correlation approximations: generalized gradient approximation (GGA), which includes the PBE functional, meta-GGA (TPSS and M06-L), and hybrid-GGA (B3LYP).…”

Probing the Chemical Bond between Lanthanides and Carbon: CeC, PrC, NdC, LuC, and TmC2

“…Accurate measurements of the BDEs of these molecules provide stringent benchmarks for newly emerging quantum chemical methodologies that aim to better predict the chemical properties of lanthanide-containing compounds. − The currently available thermochemical data for lanthanide-containing compounds are scarce in quantity and have large error limits; in some cases, they have been obtained purely on the basis of previously defined trends . These limitations on the currently available data have led to the adoption of a 5 kcal/mol standard for achieving “experimental accuracy” in computations on lanthanide species, a greatly relaxed standard for experimental accuracy than the 1 kcal/mol standard first proposed by Pople for main-group compounds .…”