Theoretical study of actinide monocarbides (ThC, UC, PuC, and AmC)

Pogány, Péter; Kovács, Attila; Visscher, Lucas; Konings, R.J.M.

doi:10.1063/1.4972812

Cited by 16 publications

(18 citation statements)

References 61 publications

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“…A direct calculation of the UC bond energy with respect to the U + C asymptote gives a value of 419.0 kJ/mol, which differs from the value given above by ∼8 kJ/mol, most likely due to the difficulty of calculating the energy of U at the CCSD(T) level. Our results for BDE(UC) at the FPD level are higher by about 0.1 eV compared to the calculated value of 402 kJ/mol obtained by Pogańy et al 14 at the SO-CASPT2 level. Note that the SO-CASPT2 calculations in the current work give a lower value of 390.0 kJ/mol (4.04 eV).…”

Section: ■ Results and Discussioncontrasting

confidence: 60%

“…At the SO-CASPT2/CBS level, the correlation of core electrons increases the excitation energy of the 5 Γ 2 state to 2110 cm −1 (Table S4) compared to the valence-only calculation (1606 cm −1 ) at the same level, both in agreement with the value obtained at the CCSD(T)/CBS level (1733 cm −1 ); these energies for the 5 Γ 2 state are consistent with the prior work for this state. 14 Thus, we do not know exactly what causes the difference in state orderings for the first two excited states but it could be due to the inclusion of a larger number of electronic states which might place the 5 H 4 lower in energy than the 5 Γ 2 state.…”

Section: ■ Results and Discussionmentioning

confidence: 96%

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Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC^+/0/–

et al. 2022

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A combination of high-level ab initio calculations and anion photoelectron detachment (PD) measurements is reported for the UC, UC–, and UC+ molecules. To better compare the theoretical values with the experimental photoelectron spectrum (PES), a value of 1.493 eV for the adiabatic electron affinity (AEA) of UC was calculated at the Feller–Peterson–Dixon (FPD) level. The lowest vertical detachment energy (VDE) is predicted to be 1.500 eV compared to the experimental value of 1.487 ± 0.035 eV. A shoulder to lower energy in the experimental PD spectrum with the 355 nm laser can be assigned to a combination of low-lying excited states of UC– and excited vibrational states. The VDEs calculated for the low-lying excited electronic states of UC at the SO-CASPT2 level are consistent with the observed additional electron binding energies at 1.990, 2.112, 2.316, and 3.760 eV. Potential energy curves for the Ω states and the associated spectroscopic properties are also reported. Compared to UN and UN+, the bond dissociation energy (BDE) of UC (411.3 kJ/mol) is predicted to be considerably lower. The natural bond orbitals (NBO) calculations show that the UC0/+/– molecules have a bond order of 2.5 with their ground-state configuration arising from changes in the oxidation state of the U atom in terms of the 7s orbital occupation: UC (5f27s1), UC– (5f27s2), and UC+ (5f27s0). The behavior of the UN and UC sequence of molecules and anions differs from the corresponding sequences for UO and UF.

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Section: ■ Results and Discussioncontrasting

confidence: 60%

Section: ■ Results and Discussionmentioning

confidence: 96%

Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC^+/0/–

et al. 2022

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“…20 The ground states for actinide monocarbides have been predicted by relativistic multireference calculations as 3 Σ + , 4 H, 5 H, 7 F, and 3 Σ + for AnC (An: Th, U, Np, Pu, and Am), respectively. 21,22 The UC 2 was identified as being a linear CUC molecule and the bent ThC 2 are energetically favored. 23 The UC 3 and PuC 3 clusters from global-minimum searching results adopt fan-like structures via the bonding of actinides to the C 3 unit.…”

Section: Introductionmentioning

confidence: 99%

“…Actinide carbides have attracted increasing interest recently due to their potential application in nuclear fast reactors and propulsion reactors. − Especially, uranium carbide exists in a variety of stoichiometric ratios as hard and refractory ceramic materials, including UC, U 2 C 3 , and UC 2 , which are stable in molecules and contain multiple bonds . The ground states for actinide monocarbides have been predicted by relativistic multireference calculations as 3 Σ + , 4 H, 5 H, 7 F, and 3 Σ + for AnC (An: Th, U, Np, Pu, and Am), respectively. , The UC 2 was identified as being a linear CUC molecule and the bent ThC 2 are energetically favored . The UC 3 and PuC 3 clusters from global-minimum searching results adopt fan-like structures via the bonding of actinides to the C 3 unit. , From then on, the actinide tetracarbide clusters (AnC 4 , An: Th, U, Np, Pu, and Am) and actinide hexacarbides (ThC n , UC 6 and PuC 6 , n = 1–7) have been theoretically predicted to possess a planar sector structure in which actinide atoms are connected to fan-shaped C 4 and C 6 , respectively. ,− Although a series of gas-phase molecular species, like An m C n + ( m = 2, n = 2–18, An = Th, U) have been produced by laser ionization of AnC 4 alloys, only An 2 C 3 and An 2 C 4 have been structurally assigned, which contain An–C 2 bonds similar to those in U(C 2 ) 2 and U(C 2 ) 3 molecules produced by the reaction of the U atom and carbon atom .…”

Section: Introductionmentioning

confidence: 99%

12-Membered Ring Carbides with Stabilization of Actinide Atoms

et al. 2022

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Actinide (Th and U) carbides as the potential nuclear fuels in nuclear reactors require basic research in order to understand the thermodynamic stability and performance of these substances. Here we report the structural characterization and bonding analyses of [C12], ThC12, and UC12 clusters via a global-minimum search combined with relativistic quantum chemistry calculations to elucidate the stability and bonding nature of An–C bonds. We predict that these [C12], ThC12, and UC12 compounds have a planar structure with C 6h , D 12h , and D 12h symmetry, respectively. [C12] has a hyperconjugation structure containing alternating single and double bonds. The significant stabilization when forming AnC12 predominantly comes from the electrostatic interaction between An4+ and [C12]4– and also from a certain degree of orbital interaction between the An 5f6d7s valence shell and [C12] π orbitals. The covalent character of the An–C bonds exhibits a direct in-plane σ-type overlap of the C 2p-derived MOs of [C12] and the An 5fϕ AO, thus leading to an unprecedented electronic configuration of d1f1 for U in UC12. Our results present an example of the novel properties that can be expected for actinide compounds and would provide the knowledge required to obtain novel structures of AnC12 in future experiments.

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“…Consequently, they form as AnN 1−x or AnC 1−x (An is actinide) compounds, where x is small (~0.1) but significant. In recent literature we find that the electronic structures for several AnC compounds have been studied with quantum-chemical methods [12].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of Plutonium Monocarbide from Anharmonic and Relativistic Theory

et al. 2020

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Thermodynamics of plutonium monocarbide is studied from first-principles theory that includes relativistic electronic structure and anharmonic lattice vibrations. Density-functional theory (DFT) is expanded to include orbital-orbital coupling in addition to the relativistic spin-orbit interaction for the electronic structure and it is combined with anharmonic, temperature dependent, lattice dynamics derived from the self-consistent ab initio lattice dynamics (SCAILD) method. The obtained thermodynamics are compared to results from simpler quasi-harmonic theory and experimental data. Formation enthalpy, specific heat, and Gibbs energy calculated from the anharmonic model are validated by direct comparison with a calculation of phase diagram (CALPHAD) assessment of PuC and sub-stochiometric PuC0.896. Overall, the theory reproduces CALPHAD results and measured data for PuC rather well, but the comparison is hampered by the sub-stoichiometric nature of plutonium monocarbide. It was found that a bare theoretical approach that ignores spin-orbit and orbital-orbital coupling (orbital polarization) of the plutonium 5f electrons promotes too soft phonons and Gibbs energies that are incompatible with that of the CALPHAD assessment of the experimental data. The investigation of PuC suggests that the electronic structure is accurately described by plutonium 5f electrons as “band like” and delocalized, but correlate through spin polarization, orbital polarization, and spin-orbit coupling, in analogy to previous findings for plutonium metal.

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Theoretical study of actinide monocarbides (ThC, UC, PuC, and AmC)

Cited by 16 publications

References 61 publications

Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC^+/0/–

Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC^+/0/–

12-Membered Ring Carbides with Stabilization of Actinide Atoms

Thermodynamics of Plutonium Monocarbide from Anharmonic and Relativistic Theory

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Theoretical study of actinide monocarbides (ThC, UC, PuC, and AmC)

Cited by 16 publications

References 61 publications

Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC+/0/–

Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC+/0/–

12-Membered Ring Carbides with Stabilization of Actinide Atoms

Thermodynamics of Plutonium Monocarbide from Anharmonic and Relativistic Theory

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Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC^+/0/–

Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC^+/0/–