Computational Tools for Predictive Modeling of Properties in Complex Actinide Systems

Autschbach, Jochen; Govind, Niranjan; Atta‐Fynn, Raymond; Bylaska, Eric J.; Weare, John W.; Jong, Wibe A. de

doi:10.1002/9781118688304.ch12

Cited by 12 publications

(11 citation statements)

References 175 publications

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“…The wavefunction may be broken down into two-component functions traditionally known as the large and small components; these may further be broken down into the spin components. [194][195][196][197] The implementation of approximate all-electron relativistic methods in quantum chemical codes requires the removal of the negative energy states and the factoring out of the spin-free terms. Both of these may be achieved using a transformation of the Dirac Hamiltonian known in general as a Foldy-Wouthuysen (FW) transformation.…”

Section: Relativistic Methodsmentioning

confidence: 99%

“…Other approaches include the zeroth order regular approximation (ZORA), [201][202][203][204] modification of the Dirac equation by Dyall, 205 which involves an exact FW transformation on the atomic basis set level, 206,207 and the exact 2-component (X2C) formulation, which is a catch-all for a variety of methods that arrive at an exactly decoupled two-component Hamiltonian using matrix algebra. 197,[208][209][210][211] NWChem contains released implementations of the DKH, ZORA, and Dyall approaches, while the X2C method is available in a development version. 209,211 Since these approximations only modify the integrals, they can, in principle, be used at all levels of theory.…”

Section: Relativistic Methodsmentioning

confidence: 99%

“…Free energy approaches are useful for simulating reactions where traditional quantum chemistry approaches can be difficult to use and often require the expertise of a very experienced quantum chemist, e.g., reactions that are complex with concerted or multi-step components and/or interact strongly with the solvent. Recent examples include solvent coordination and hydrolysis of actinides metals 197,[278][279][280][281] (see Fig. 3), hydrolysis of explosives, 234 and FIG.…”

Section: The Journal Of Chemical Physicsmentioning

confidence: 99%

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NWChem: Past, present, and future

Aprà

Bylaska

Jong

et al. 2020

The Journal of Chemical Physics

523

289

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Specialized computational chemistry packages have permanently reshaped the landscape of chemical and materials science by providing tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties. In this regard, electronic structure packages have played a special role by using first-principle-driven methodologies to model complex chemical and materials processes. Over the past few decades, the rapid development of computing technologies and the tremendous increase in computational power have offered a unique chance to study complex transformations using sophisticated and predictive many-body techniques that describe correlated behavior of electrons in molecular and condensed phase systems at different levels of theory. In enabling these simulations, novel parallel algorithms have been able to take advantage of computational resources to address the polynomial scaling of electronic structure methods. In this paper, we briefly review the NWChem computational chemistry suite, including its history, design principles, parallel tools, current capabilities, outreach, and outlook.

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Section: Relativistic Methodsmentioning

confidence: 99%

Section: Relativistic Methodsmentioning

confidence: 99%

Section: The Journal Of Chemical Physicsmentioning

confidence: 99%

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NWChem: Past, present, and future

Aprà

Bylaska

Jong

et al. 2020

The Journal of Chemical Physics

523

289

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“…The identification and characterization of covalent chemical bonding involving the valence d or f orbitals of a metal ion in a complex is of major interest in chemistry. − However, consensus regarding the extent of the participation of lanthanide (Ln) 4f and actinide (An) 5f orbitals in covalent bonding has only partly been reached. It is clear that these orbitals are involved to some degree in covalent bonding, especially for the early Ln/An ions and much more so for An than for Ln.…”

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confidence: 99%

Ab Initio Study of Covalency in the Ground versus Core-Excited States and X-ray Absorption Spectra of Actinide Complexes

Sergentu

Duignan

Autschbach

2018

J. Phys. Chem. Lett.

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130

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Relativistic multireference ab initio wave function calculations within the restricted active space (RAS) framework were performed to calculate metal and ligand X-ray absorption (XAS) near-edge spectroscopy (XANES) intensities for the metal M edges of [PuO(HO)], [AnO] (An = U, Np, Pu), and [AmCl] and the Cl K edge of the Am complex. The extent of An(5f)-ligand bonding was determined via natural localized molecular orbital analyses of the relevant spin-orbit coupled multireference states. The calculated spectra are in good agreement with experiments and allow a detailed assignment of the observed spectral features. The XANES M-edge spectra are representative of the actinide orbital covalency in the probed core-excited states, which may be different from the ground-state covalency. An assignment of ground-state An orbital covalency based on XAS spectra should therefore be made with caution.

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“…Scalar relativistic approaches such as the zero-order regular approximation (ZORA) [28], and the Douglas-Kroll Hamiltonian (DKH) [29] are implemented in a number of quantum chemistry packages. ZORA only holds for basis functions that are independent of the perturbation, which theoretically precludes using GIAOs, although in practice the error introduced is small for large basis sets [30].…”

Section: The Orbital Shielding Tensor σ Orbmentioning

confidence: 99%

Modelling the Effect of Zero-Field Splitting on the 1H, 13C and 29Si Chemical Shifts of Lanthanide and Actinide Compounds

2019

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The prediction of paramagnetic NMR (pNMR) chemical shifts in molecules containing heavy atoms presents a significant challenge to computational quantum chemistry. The importance of meeting this challenge lies in the central role that NMR plays in the structural characterisation of chemical systems. Hence there is a need for reliable assignment and prediction of chemical shifts. In a previous study [Trends in Physical Chemistry, 17, 25–57, (2017)] we looked at the computation of pNMR chemical shifts in lanthanide and actinide complexes using a spin Hamiltonian approach. In that study we were principally concerned with molecules with S = 1/2 ground states. In the present work we extend that study by looking at the effect of zero field splitting (ZFS) for six complexes with S = 3/2 ground states. It is shown that the inclusion of ZFS can produce substantial shifts in the predicted chemical shifts. The computations presented are typically sufficient to enable assignment of experimental spectra. However for one case, in which the peaks are closely clustered, the inclusion of ZFS re-orders the chemical shifts making assignment quite difficult. We also observe, and echo, the previously reported importance of including the paramagnetic spin-orbit hyperfine interaction for 13 C and 29 Si atoms, when these are directly bound to a heavy element and thus subject to heavy-atom-light-atom effects. The necessary computations are very demanding, and more work is needed to find theoretical and computational approaches that simplify the evaluation of this term. We discuss the computation of each term required in the spin Hamiltonian. The systems we study in this work are restricted to a single heavy atom ion (one Nd(III) and five U(III) complexes), but typify some of the computational complexity encountered in lanthanide and actinide containing molecules.

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Computational Tools for Predictive Modeling of Properties in Complex Actinide Systems

Cited by 12 publications

References 175 publications

NWChem: Past, present, and future

NWChem: Past, present, and future

Ab Initio Study of Covalency in the Ground versus Core-Excited States and X-ray Absorption Spectra of Actinide Complexes

Modelling the Effect of Zero-Field Splitting on the 1H, 13C and 29Si Chemical Shifts of Lanthanide and Actinide Compounds

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