Excited States of Large Open-Shell Molecules: An Efficient, General, and Spin-Adapted Approach Based on a Restricted Open-Shell Ground State Wave function

Roemelt, Michael; Neese, Frank

doi:10.1021/jp3126126

Cited by 89 publications

(81 citation statements)

References 89 publications

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“…Calculations of NEXAS spectra are challenging, and require computational methods that explicitly account for the excitations of core-level electrons, orbital relaxation effects, and electron correlation. 8 Several theoretical approaches have been adapted to compute core-valence excitations, including: scaled-opposite-spin configuration interaction singles with perturbative doubles [SOS-CIS(D)], 9 a restricted open-shell DFT/CIS method, 10,11 second-order algebraic diagrammatic construction [ADC(2)], 12,13 multiple scattering X α methods 14 , a maximum overlap ΔSCF approach, 15 a restricted active space SCF method (RASSCF), 16 transition potential theory, 17 coupled-cluster response theory, 8 time-dependent density functional theory (TDDFT), 18 and restricted excitation window TDDFT (REW-TDDFT). 19 Among these methods, TDDFT is perhaps the most attractive option because of its reduced computational cost and ability to calculate multiple excited states.…”

Section: Introductionmentioning

confidence: 99%

Simulation of X-ray absorption spectra with orthogonality constrained density functional theory

Derricotte

Evangelista

2015

Phys. Chem. Chem. Phys.

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Orthogonality constrained density functional theory (OCDFT) is a variational time-independent approach for the computation of electronic excited states. In this work we extend OCDFT to compute core-excited states and generalize the original formalism to determine multiple excited states. Benchmark computations on a set of 13 small molecules and 40 excited states show that unshifted OCDFT/B3LYP excitation energies have a mean absolute error of 1.0 eV. Contrary to time-dependent DFT, OCDFT excitation energies for first- and second-row elements are computed with near-uniform accuracy. OCDFT core excitation energies are insensitive to the choice of the functional and the amount of Hartree–Fock exchange. We show that OCDFT is a powerful tool for the assignment of X-ray absorption spectra of large molecules by simulating the gas-phase near-edge spectrum of adenine and thymine.

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Section: Introductionmentioning

confidence: 99%

Simulation of X-ray absorption spectra with orthogonality constrained density functional theory

Derricotte

Evangelista

2015

Phys. Chem. Chem. Phys.

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“…[27][28][29][30][31][32][33][34] Density functional theory (DFT) based techniques are becoming a more popular tool, though multiplets as they are found in spectroscopic experiments do not straightforwardly emerge from the calculations. [45][46][47] Although advances in quantum mechanical calculations are promising, a vast amount of computer power and user experience is necessary to yield trustworthy results. Canning luminescent properties of a multitude of scintillators, based on the Ce 3+ and Eu 2+ ions within the DFT + U formalism.…”

Section: Introductionmentioning

confidence: 99%

Energy level modeling of lanthanide materials: review and uncertainty analysis

Joos

Poelman

Smet

2015

Phys. Chem. Chem. Phys.

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Energy level schemes are an essential tool for the description and interpretation of atomic spectra. During the last 40 years, several empirical methods and relationships were devised for constructing energy level schemes of lanthanide defects in wide band gap solids, culminating in the chemical shift model by Thiel and Dorenbos. This model allows us to calculate the electronic and optical properties of the considered materials. However, an unbiased assessment of the accuracy of the obtained values of the calculated parameters is still lacking to a large extent. In this paper, error margins for calculated electronic and optical properties are deduced. It is found that optical transitions can be predicted within an acceptable error margin, while the description of phenomena involving conduction band states is limited to qualitative interpretation due to the large error margins for physical observables such as thermal quenching temperature, corresponding to standard deviations in the range 0.3-0.5 eV for the relevant energy differences. As an example, the electronic structure of lanthanide doped calcium thiogallate (CaGa2S4) is determined, taking the experimental spectra of CaGa2S4:Ln(Q+) (Ln(Q+) = Ce(3+), Eu(2+), Tm(3+)) as input. Two different approaches to obtain the shape of the zig-zag curves connecting the 4f levels of the different lanthanides are explored and compared.

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“…The spin-orbit and spin-spin interactions were treated at the quasi-degenerate 155 perturbation theory (QDPT) level [55], both for the equilibrium geometry and the dissociated molecule. The spin-spin interaction will not be reported in what follows, since its contribution is negligibly small.…”

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confidence: 99%

Binary and ternary Po-containing molecules relevant for LBE cooled reactors at operating temperature

Deyne

Rijpstra

Waroquier

et al. 2015

Journal of Nuclear Materials

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Quantum-chemical calculations at several levels of theory were used to assess the stability at different temperatures of a set of 13 binary and ternary Pocontaining molecules that could possibly be formed in an environment with lead, bismuth, oxygen and water. These are conditions that are relevant for a heavy liquid metal cooled fission reactor. The conclusions are that especially PoPb, PbPoO and PoOH and to a lesser extent Po 2 and PoO are stable. These small molecules are likely to be found near the Lead-Bismuth-Eutectic (LBE) coolant at operational temperatures. In contrast Po 3 and PoBi are unlikely to be present under the assumed conditions. Several stability criteria, such as the dissociation into free atoms or into molecular fragments at realistic Poconcentrations or in the thermodynamic limit are discussed at different temperatures. The results obtained with a medium level of theory (Density Functional Theory, PBE0 with Relativistic Effective Core Potentials) show good qualitative correspondence with calculations performed at a much higher level of theory (Multi Reference Configuration Interaction, with spin-orbit coupling and scalar relativistic Hamiltonian). This makes the medium level of theory to be a fair alternative, for obtaining at least qualitative insight, for a high level calculation method which is unfeasible for much larger systems.

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Excited States of Large Open-Shell Molecules: An Efficient, General, and Spin-Adapted Approach Based on a Restricted Open-Shell Ground State Wave function

Cited by 89 publications

References 89 publications

Simulation of X-ray absorption spectra with orthogonality constrained density functional theory

Simulation of X-ray absorption spectra with orthogonality constrained density functional theory

Energy level modeling of lanthanide materials: review and uncertainty analysis

Binary and ternary Po-containing molecules relevant for LBE cooled reactors at operating temperature

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