Jonathan D Gledhill, Michael J G Peach, David J Tozer Assessment of Tuning Methods for Enforcing Approximate Energy Linearity in Range-Separated Hybrid Functionals (Article) J. Chem. Theory Comput., 9, 10, Page(s): 4414-4420, 2013. (Abstract | Links | BibTeX) @article{gledhill:4414,
name = {Assessment of Tuning Methods for Enforcing Approximate Energy Linearity in Range-Separated Hybrid Functionals},
author = {Jonathan D Gledhill, Michael J G Peach, David J Tozer},
url = {http://pubs.acs.org/doi/abs/10.1021/ct400592a},
year = {2013},
date = {2013-08-22},
journal = {J. Chem. Theory Comput.},
volume = {9},
number = {10},
pages = {4414-4420},
abstract = {A range of tuning methods, for enforcing approximate energy linearity through a system-by-system optimization of a range-separated hybrid functional, are assessed. For a series of atoms, the accuracy of the frontier orbital energies, ionization potentials, electron affinities, and orbital energy gaps is quantified, and particular attention is paid to the extent to which approximate energy linearity is actually achieved. The tuning methods can yield significantly improved orbital energies and orbital energy gaps, compared to those from conventional functionals. For systems with integer M electrons, optimal results are obtained using a tuning norm based on the highest occupied orbital energy of the M and M + 1 electron systems, with deviations of just 0.1–0.2 eV in these quantities, compared to exact values. However, detailed examination for the carbon atom illustrates a subtle cancellation between errors arising from nonlinearity and errors in the computed ionization potentials and electron affinities used in the tuning.},
}
A range of tuning methods, for enforcing approximate energy linearity through a system-by-system optimization of a range-separated hybrid functional, are assessed. For a series of atoms, the accuracy of the frontier orbital energies, ionization potentials, electron affinities, and orbital energy gaps is quantified, and particular attention is paid to the extent to which approximate energy linearity is actually achieved. The tuning methods can yield significantly improved orbital energies and orbital energy gaps, compared to those from conventional functionals. For systems with integer M electrons, optimal results are obtained using a tuning norm based on the highest occupied orbital energy of the M and M + 1 electron systems, with deviations of just 0.1–0.2 eV in these quantities, compared to exact values. However, detailed examination for the carbon atom illustrates a subtle cancellation between errors arising from nonlinearity and errors in the computed ionization potentials and electron affinities used in the tuning. |
Robert M. Edkins, Katharina Fucke, Michael J. G. Peach, Andrew G. Crawford, Todd B. Marder, Andrew Beeby Syntheses, Structures, and Comparison of the Photophysical Properties of Cyclometalated Iridium Complexes Containing the Isomeric 1- and 2-(2′-pyridyl)pyrene Ligands (Article) Inorg. Chem., 52, 17, Page(s): 9842–9860, 2013. (Abstract | Links | BibTeX) @article{peach:9842,
name = {Syntheses, Structures, and Comparison of the Photophysical Properties of Cyclometalated Iridium Complexes Containing the Isomeric 1- and 2-(2′-pyridyl)pyrene Ligands},
author = {Robert M. Edkins, Katharina Fucke, Michael J. G. Peach, Andrew G. Crawford, Todd B. Marder, Andrew Beeby},
url = {http://pubs.acs.org/doi/abs/10.1021/ic400819f},
year = {2013},
date = {2013-08-14},
journal = {Inorg. Chem.},
volume = {52},
number = {17},
pages = {9842–9860},
abstract = {Two cyclometalated iridium complexes of the form IrL2(acac) have been synthesized, where L is either of the isomeric ligands 1- or 2-(2′-pyridyl)pyrene (1-pypyrH or 2-pypyrH). These complexes have been investigated in terms of their photophysical behavior and, although both complexes exhibit similar pure radiative lifetimes, they have substantially different observed phosphorescence lifetimes and quantum yields. Moreover, the observed phosphorescence lifetimes and quantum yields of both complexes, as well as the absorption spectra of Ir(1-pypyr)2(acac), exhibit a strong solvent dependence, while there is essentially no solvatochromism in the emission spectra of either complex. Single-crystal X-ray diffraction studies of both ligands and both iridium complexes reveal structural differences between the two isomers. The crystal structures of the ligands, supported by density functional theory (DFT) modeling, show that a twist is present between the pyridyl and pyrenyl rings in 1-pypyrH, but is absent in 2-pypyrH, which leads to the requirement for more unusual cyclometalation conditions for 1-pypyrH. Furthermore, it is suggested that the strained structure of Ir(1-pypyr)2(acac) provides access to a facile nonradiative excited state deactivation pathway, which leads to the higher value of knr for this isomer. DFT, TD-DFT, and ΔSCF calculations have been conducted to investigate further the photophysical properties of the complexes, allowing a detailed comparison of the two isomers. We find that Tamm-Dancoff Approximation TD-DFT with the CAM-B3LYP functional provides the best agreement between experimentally and theoretically determined transition energies, performing better than the more common combination of TD-DFT with B3LYP, the reasons for which are outlined. We also highlight some difficulties with performing optimization calculations on oxidized complexes to assess electrochemical data.},
}
Two cyclometalated iridium complexes of the form IrL2(acac) have been synthesized, where L is either of the isomeric ligands 1- or 2-(2′-pyridyl)pyrene (1-pypyrH or 2-pypyrH). These complexes have been investigated in terms of their photophysical behavior and, although both complexes exhibit similar pure radiative lifetimes, they have substantially different observed phosphorescence lifetimes and quantum yields. Moreover, the observed phosphorescence lifetimes and quantum yields of both complexes, as well as the absorption spectra of Ir(1-pypyr)2(acac), exhibit a strong solvent dependence, while there is essentially no solvatochromism in the emission spectra of either complex. Single-crystal X-ray diffraction studies of both ligands and both iridium complexes reveal structural differences between the two isomers. The crystal structures of the ligands, supported by density functional theory (DFT) modeling, show that a twist is present between the pyridyl and pyrenyl rings in 1-pypyrH, but is absent in 2-pypyrH, which leads to the requirement for more unusual cyclometalation conditions for 1-pypyrH. Furthermore, it is suggested that the strained structure of Ir(1-pypyr)2(acac) provides access to a facile nonradiative excited state deactivation pathway, which leads to the higher value of knr for this isomer. DFT, TD-DFT, and ΔSCF calculations have been conducted to investigate further the photophysical properties of the complexes, allowing a detailed comparison of the two isomers. We find that Tamm-Dancoff Approximation TD-DFT with the CAM-B3LYP functional provides the best agreement between experimentally and theoretically determined transition energies, performing better than the more common combination of TD-DFT with B3LYP, the reasons for which are outlined. We also highlight some difficulties with performing optimization calculations on oxidized complexes to assess electrochemical data. |
Michael J. G. Peach, Neil Warner, David J. Tozer On the triplet instability in TDDFT (Article) Mol. Phys., 111, 9-11, Page(s): 1271-1274, 2013. (Abstract | BibTeX) @article{peach:1271,
name = {On the triplet instability in TDDFT},
author = {Michael J. G. Peach, Neil Warner, David J. Tozer},
year = {2013},
date = {2013-04-09},
journal = {Mol. Phys.},
volume = {111},
number = {9-11},
pages = {1271-1274},
abstract = {The utility of a Hartree–Fock triplet stability threshold, for identifying time-dependent density functional theory triplet excitations for which the inclusion of exact orbital exchange is detrimental, is illustrated for a benchmark set of 63 excitations in 20 organic molecules. Following earlier spin–spin coupling observations that suggest a relatively small triplet instability problem, the accuracy of triplet excitation energies from the B97-2 hybrid functional is also quantified. As anticipated, the results are relatively accurate and this is readily understood in terms of the stabilities. Application of the Tamm–Dancoff approximation dramatically improves all the triplet excitation energies corresponding to low stabilities, whilst also providing a modest improvement in the corresponding singlet states.},
}
The utility of a Hartree–Fock triplet stability threshold, for identifying time-dependent density functional theory triplet excitations for which the inclusion of exact orbital exchange is detrimental, is illustrated for a benchmark set of 63 excitations in 20 organic molecules. Following earlier spin–spin coupling observations that suggest a relatively small triplet instability problem, the accuracy of triplet excitation energies from the B97-2 hybrid functional is also quantified. As anticipated, the results are relatively accurate and this is readily understood in terms of the stabilities. Application of the Tamm–Dancoff approximation dramatically improves all the triplet excitation energies corresponding to low stabilities, whilst also providing a modest improvement in the corresponding singlet states. |
