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Orthogonality constrained density functional theory (OCDFT) provides near-edge X-ray absorption (NEXAS) spectra of first-row elements within one electronvolt from experimental values. However, with increasing atomic number, scalar relativistic effects become the dominant source of error in a nonrelativistic OCDFT treatment of core-valence excitations. In this work we report a novel implementation of the spin-free exact-two-component (X2C) one-electron treatment of scalar relativistic effects and its combination with a recently developed OCDFT approach to compute a manifold of core-valence excited states. The inclusion of scalar relativistic effects in OCDFT reduces the mean absolute error of second-row elements core-valence excitations from 10.3 to 2.3 eV. For all the excitations considered, the results from X2C calculations are also found to be in excellent agreement with those from low-order spin-free Douglas-Kroll-Hess relativistic Hamiltonians. The X2C-OCDFT NEXAS spectra of three organotitanium complexes (TiCl4, TiCpCl3, TiCp2Cl2) are in very good agreement with unshifted experimental results and show a maximum absolute error of 5-6 eV. In addition, a decomposition of the total transition dipole moment into partial atomic contributions is proposed and applied to analyze the nature of the Ti pre-edge transitions in the three organotitanium complexes.

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“…The mean absolute error (MAE) is also reported for each method. Experimental values are from refs − .…”

Section: Resultsmentioning

confidence: 99%

“…The geometries of the test set molecules were optimized with nonrelativistic DFT using Becke’s B3LYP − exchange-correlation functional and the def2-QZVP , basis set. Individual excitation energies are compared with data obtained from gas-phase NEXAS experiments. − …”

Section: Computational Detailsmentioning

confidence: 99%

Predicting Near Edge X-ray Absorption Spectra with the Spin-Free Exact-Two-Component Hamiltonian and Orthogonality Constrained Density Functional Theory

Verma

Derricotte

Evangelista

2015

J. Chem. Theory Comput.

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“…Table 1 summarizes the performance of OCDFT by reporting the mean absolute error (MAE) in the excitation energy for 12 unique combinations of basis set and density functionals. Individual excitation energies computed with OCDFT and TDDFT are compared to values from gas-phase NEXAS experiments [69][70][71][72][73][74][75][76][77][78][79][80][81][82][83] in Tables 2 and 3. Table 2 displays excitations from first-row elements, while Table 3 shows excitations from second-row elements.…”

Section: Calibration Of Ocdft Core-excitation Energiesmentioning

confidence: 99%

“…The OCDFT and TDDFT results are reported here as deviations from the experimental value in electron volts (eV), mean absolute error (MAE) is also reported for each method. Experimental values are from ref [78][79][80][81][82][83].…”

mentioning

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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“…Deviations from experiment shown in parenthesis. Experimental data from ref [66][67][68][69][70][71].…”

mentioning

confidence: 99%

Time-dependent density functional theory calculations of near-edge X-ray absorption fine structure with short-range corrected functionals

Besley

Peach

Tozer

2009

Phys. Chem. Chem. Phys.

202

304

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We report calculations of core excitation energies and near-edge X-ray absorption fine structure (NEXAFS) spectra computed with time-dependent density functional theory (TDDFT). TDDFT with generalized gradient approximation and standard hybrid exchange-correlation functionals is known to underestimate core excitation energies. This failure is shown to be associated with the self-interaction error at short interelectronic distances. Short-range corrected hybrid functionals are shown to reduce the error in the computed core excitation energies for first and second row nuclei in a range of molecules to a level approaching that observed in more traditional excited states calculations in the ultraviolet region. NEXAFS spectra computed with the new functionals agree well with experiment and the pre-edge features in the NEXAFS spectra of plastocyanin are correctly predicted.

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Angle-resolved two-dimensional mapping of electron emission from the inner-shell2pexcitations inCl2

Cited by 14 publications

References 23 publications

Predicting Near Edge X-ray Absorption Spectra with the Spin-Free Exact-Two-Component Hamiltonian and Orthogonality Constrained Density Functional Theory

Predicting Near Edge X-ray Absorption Spectra with the Spin-Free Exact-Two-Component Hamiltonian and Orthogonality Constrained Density Functional Theory

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

Time-dependent density functional theory calculations of near-edge X-ray absorption fine structure with short-range corrected functionals

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