Ab Initio Composite Approaches for Heavy Element Energetics: Ionization Potentials for the Actinide Series of Elements

Abstract

The first, second, and third gas-phase ionization potentials have been determined for the actinide series of elements using an ab initio composite scalar and fully relativistic approach, employing the coupled cluster with single, double, and perturbative triple excitations (CCSD­(T)) and Dirac Hartree–Fock (DHF) methods, extrapolated to the complete basis set (CBS) limit. The impact of electron correlation and basis set choice within this framework are examined. Additionally, the first three ionization potentials were obtained using an ab initio heavy element correlation-consistent Composite Approach (here referred to as α-ccCA). This is the first utilization of a ccCA for actinide species.

Route to Chemical Accuracy for Computational Uranium Thermochemistry

“…The final computed result for the first ionization energy agrees reasonably well with the experimental value, with a remaining discrepancy of around 13 kJ/mol attributed to the residue dynamic correlation effects. North and Wilson 57 have recently reported calculations of the ionization energies for the actinide atoms using additivity schemes based on scalarrelativistic coupled-cluster calculations augmented with spin− orbit corrections. The study has obtained good agreement with experimental ionization energies for most actinide atoms with the uranium atom being a notable exception.…”

“…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. ,,,− …”

On the potentially transformative role of auxiliary-field quantum Monte Carlo in quantum chemistry: A highly accurate method for transition metals and beyond

“…[88][89][90] Recent progress in all-electron basis set development and composite correlated wavefunction approaches appear more promising. [91][92][93][94] Ref. 95 presents a relativistic many-body formalism to perform ph-AFQMC calculations on two-component Hamiltonians which include an explicit treatment of SOC.…”