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Francisco J. Hidalgo - One of the best experts on this subject based on the ideXlab platform.
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ab initio Electronic Circular Dichroism of fullerenes single walled carbon nanotubes and ligand protected metal nanoparticles
Chirality, 2014Co-Authors: Cecilia Noguez, Francisco J. HidalgoAbstract:The versatility and applicability of a time-perturbed density functional method implemented within the SIESTA program package to calculate Electronic Circular Dichroism of diverse nanoparticles is discussed. Results for nanostructures, such as fullerenes, single-wall carbon nanotubes, as well as metallic nanoparticles composed of up to hundreds of atoms were examined by comparison with previously reported experimental and theoretical results. In all cases, the calculated Electronic Circular Dichroism shows very good consistency with other calculations, and a remarkable agreement with experiments. It is concluded that such a high-level method provides theoretical support for the quantification, understanding, and prediction of chirality and its measurement in nanostructures. It is expected that this information would be useful to motivate further experimental studies and interpretation of optical activity in terms of Electronic Circular Dichroism in novel nanostructures. Chirality 26:553–562, 2014. © 2014 Wiley Periodicals, Inc.
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Ab Initio Electronic Circular Dichroism of Fullerenes, Single‐Walled Carbon Nanotubes, and Ligand‐Protected Metal Nanoparticles
Chirality, 2014Co-Authors: Cecilia Noguez, Francisco J. HidalgoAbstract:The versatility and applicability of a time-perturbed density functional method implemented within the SIESTA program package to calculate Electronic Circular Dichroism of diverse nanoparticles is discussed. Results for nanostructures, such as fullerenes, single-wall carbon nanotubes, as well as metallic nanoparticles composed of up to hundreds of atoms were examined by comparison with previously reported experimental and theoretical results. In all cases, the calculated Electronic Circular Dichroism shows very good consistency with other calculations, and a remarkable agreement with experiments. It is concluded that such a high-level method provides theoretical support for the quantification, understanding, and prediction of chirality and its measurement in nanostructures. It is expected that this information would be useful to motivate further experimental studies and interpretation of optical activity in terms of Electronic Circular Dichroism in novel nanostructures. Chirality 26:553–562, 2014. © 2014 Wiley Periodicals, Inc.
Stefan Grimme - One of the best experts on this subject based on the ideXlab platform.
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Electronic Circular Dichroism of highly conjugated π-systems: breakdown of the Tamm-Dancoff/configuration interaction singles approximation.
The journal of physical chemistry. A, 2015Co-Authors: Christoph Bannwarth, Stefan GrimmeAbstract:We show that the Electronic Circular Dichroism (ECD) of delocalized π-systems represents a worst-case scenario for Tamm–Dancoff approximated (TDA) linear response methods. We mainly consider density functional theory (TDA-DFT) variants together with range-separated hybrids, but the conclusions also apply for other functionals as well as the configuration interaction singles (CIS) approaches. We study the effect of the TDA for the computation of ECD spectra in some prototypical extended π-systems. The C76 fullerene, a chiral carbon nanotube fragment, and [11]helicene serve as model systems for inherently chiral, π-chromophores. Solving the full linear response problem is inevitable in order to obtain accurate ECD spectra for these systems. For the C76 fullerene and the nanotube fragment, TDA and CIS approximated methods yield spectra in the origin-independent velocity gauge formalism of incorrect sign which would lead to the assignment of the opposite (wrong) absolute configuration. As a counterexample, we...
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Electronic Circular Dichroism of highly conjugated π systems breakdown of the tamm dancoff configuration interaction singles approximation
Journal of Physical Chemistry A, 2015Co-Authors: Christoph Bannwarth, Stefan GrimmeAbstract:We show that the Electronic Circular Dichroism (ECD) of delocalized π-systems represents a worst-case scenario for Tamm–Dancoff approximated (TDA) linear response methods. We mainly consider density functional theory (TDA-DFT) variants together with range-separated hybrids, but the conclusions also apply for other functionals as well as the configuration interaction singles (CIS) approaches. We study the effect of the TDA for the computation of ECD spectra in some prototypical extended π-systems. The C76 fullerene, a chiral carbon nanotube fragment, and [11]helicene serve as model systems for inherently chiral, π-chromophores. Solving the full linear response problem is inevitable in order to obtain accurate ECD spectra for these systems. For the C76 fullerene and the nanotube fragment, TDA and CIS approximated methods yield spectra in the origin-independent velocity gauge formalism of incorrect sign which would lead to the assignment of the opposite (wrong) absolute configuration. As a counterexample, we...
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Calculation of Electronic Circular Dichroism Spectra with Time-Dependent Double-Hybrid Density Functional Theory
The journal of physical chemistry. A, 2009Co-Authors: Lars Goerigk, Stefan GrimmeAbstract:Time-dependent double-hybrid density functional theory is applied to the calculation of the Electronic Circular Dichroism (CD) spectra of molecules. The TD-B2PLYP method is based on vertical excitation energies obtained from its hybrid-GGA part B2LYP in a conventional TD-DFT linear response treatment and a CIS(D) type perturbation correction for these excited states. A new benchmark set of six representative organic molecules with a wide variety of different Electronic character is introduced for this investigation. The simulated TD-B2PLYP spectra are compared to experiment and those computed with the TD-B2LYP (i.e., no CIS(D) correction) and TD-B3LYP methods. Vertical excitation energies at the perturbatively corrected level are, in the majority of cases, more accurate than, e.g., with TD-B3LYP. Relative band positions are also reproduced better. In one example, the high-energy CD bands are not computed with sufficient accuracy, which is attributed to an instability of the perturbation correction. Due to...
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systematic investigation of modern quantum chemical methods to predict Electronic Circular Dichroism spectra
Journal of Physical Chemistry A, 2003Co-Authors: Christian Diedrich, Stefan GrimmeAbstract:The ability of different quantum chemical methods to predict experimental Electronic Circular Dichroism (CD) spectra is critically evaluated. Two single-reference, time-dependent approaches based either on density functional theory (TDDFT) or a simplified coupled-cluster expansion (CC2) and two multireference methods (MRMP2 and DFT/MRCI) are considered. The methods are applied to a test suite of seven molecules including a wide range of difficult chromophores (“real-life” examples) and to three model systemsH2S2, twisted ethylene, and dimethyloxiranewhere accurate ab initio MRCI reference data are used for comparison. To investigate the effect of “exact” exchange mixing systematically, the TDDFT calculations were carried out with the BP86, B3-LYP, and BH-LYP functionals. The time-dependent Hartree−Fock (TDHF) method was included as an “upper limit” for the HF-exchange part in the functional. In general, it is found that the accuracy of most of the simulated spectra (except those from TDHF) is good enough ...
Vincenzo Barone - One of the best experts on this subject based on the ideXlab platform.
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Simulation of Vacuum UV Absorption and Electronic Circular Dichroism Spectra of Methyl Oxirane: The Role of Vibrational Effects
Journal of chemical theory and computation, 2016Co-Authors: Manuel Hodecker, Malgorzata Biczysko, Andreas Dreuw, Vincenzo BaroneAbstract:Vibrationally resolved one-photon absorption and Electronic Circular Dichroism spectra of (R)-methyl oxirane were calculated with different Electronic and vibronic models selecting, through an analysis of the convergence of the results, the best compromise between reliability and computational cost. Linear-response TD-DFT/CAM-B3LYP/SNST Electronic computations in conjunction with the simple vertical gradient vibronic model were chosen and employed for systematic comparison with the available experimental data. Remarkable agreement between simulated and experimental spectra was achieved for both one-photon absorption and Circular Dichroism concerning peak positions, relative intensities, and general spectral shapes considering the computational efficiency of the chosen theoretical approach. The significant improvement of the results with respect to smearing of vertical Electronic transitions by phenomenological Gaussian functions and the possible inclusion of solvent effects by polarizable continuum models...
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Vibronic Coupling Dominates the Electronic Circular Dichroism of the Benzene Chromophore 1Lb band
The Journal of organic chemistry, 2013Co-Authors: Gennaro Pescitelli, Lorenzo Di Bari, Antonio Rizzo, Vincenzo Barone, Fabrizio SantoroAbstract:The alkylbenzene derivatives (R)-PhCH(CH3)tBu (1) and (R)-PhCH(CH3)iPr (2) were taken as paradigms of chiral benzene compounds and their vibronic Electronic Circular Dichroism (ECD) spectrum in the 1Lb band region analyzed in detail. The 1Lb ECD band of chiral benzene compounds is often used to assign absolute configurations on the basis of sector rules. However, 1Lb ECD bands of several benzene derivatives are associated with a forbidden character and show marked vibrational progressions strongly modulating their shape. This is also true for compounds 1 and 2, the latter also showing a peculiar thermochromism. The low-temperature ECD spectrum of 2 displays in fact an alternation of positive and negative ECD maxima. Vibronic ECD calculations performed within a TDDFT scheme allowed a full rationalization of the observed ECD spectra of 1 and 2. Especially in the case of 2, the ECD spectrum in the 1Lb band region results from a complex balance of Franck–Condon and Herzberg–Teller effects, as well as of confo...
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computational approach to the study of the lineshape of absorption and Electronic Circular Dichroism spectra
International Journal of Quantum Chemistry, 2010Co-Authors: Fabrizio Santoro, Vincenzo BaroneAbstract:In this contribution we review our recent method to compute vibrationally resolved Electronic spectra and we introduce some generalizations of the algorithm for application to Electronic Circular Dichroism. We present applications to different spectroscopies and systems, dealing both with strong and weak transitions, and addressing in detail the effect of temperature. The reported examples document that, when coupled with a proper description of the Electronic states by density functional theory and its time-dependent extension for excited states, our method is versatile and provides reliable results also for sizeable systems, allowing a detailed interpretation of their spectral features. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010
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Vibronically Resolved Electronic Circular Dichroism Spectra of (R)-(+)-3-Methylcyclopentanone: A Theoretical Study
The journal of physical chemistry. A, 2008Co-Authors: Na Lin, Fabrizio Santoro, Xian Zhao, Antonio Rizzo, Vincenzo BaroneAbstract:The vibrationally resolved Electronic Circular Dichroism (ECD) spectra of the two dominant conformers of (R)-(+)-3-methylcyclopentanone in gas phase are computed by density functional response theory, with a full account of Franck-Condon and Herzberg-Teller vibrational contributions at the harmonic level. Proper inclusion of the latter contributions was made possible by the recent implementation of effective-scaling computations of vibrational overlaps and of analytical gradients of time dependent DFT. The Coulomb-attenuated Becke three parameters Lee-Yang-Parr (CAM-B3LYP) functional reproduces both the position and the intensity of the experimental peaks, providing a remarkable improvement over the spectra obtained with the popular hybrid B3LYP functional, and allowing a confident assignment of the CD fine vibrational structure. Franck-Condon and Herzberg-Teller contributions are discussed in detail. The computed decrease of the CD intensity in the gas phase upon increase of the temperature of the sample follows the trend observed experimentally in different solvents.
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vibronically resolved Electronic Circular Dichroism spectra of r 3 methylcyclopentanone a theoretical study
Journal of Physical Chemistry A, 2008Co-Authors: Na Lin, Fabrizio Santoro, Xian Zhao, Antonio Rizzo, Vincenzo BaroneAbstract:The vibrationally resolved Electronic Circular Dichroism (ECD) spectra of the two dominant conformers of (R)-(+)-3-methylcyclopentanone in gas phase are computed by density functional response theory, with a full account of Franck-Condon and Herzberg-Teller vibrational contributions at the harmonic level. Proper inclusion of the latter contributions was made possible by the recent implementation of effective-scaling computations of vibrational overlaps and of analytical gradients of time dependent DFT. The Coulomb-attenuated Becke three parameters Lee-Yang-Parr (CAM-B3LYP) functional reproduces both the position and the intensity of the experimental peaks, providing a remarkable improvement over the spectra obtained with the popular hybrid B3LYP functional, and allowing a confident assignment of the CD fine vibrational structure. Franck-Condon and Herzberg-Teller contributions are discussed in detail. The computed decrease of the CD intensity in the gas phase upon increase of the temperature of the sample follows the trend observed experimentally in different solvents.
Fabrizio Santoro - One of the best experts on this subject based on the ideXlab platform.
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Excitonic Model for Strongly Coupled Multichromophoric Systems: The Electronic Circular Dichroism Spectra of Guanine Quadruplexes as Test Cases.
Journal of chemical theory and computation, 2020Co-Authors: James A. Green, Fabrizio Santoro, Haritha Asha, Roberto ImprotaAbstract:We here propose a general and flexible approach, based on fragment diabatization, which incorporates charge transfer states and significantly increases the reliability of excitonic Hamiltonians for systems where the chromophores are very close. This model (FrDEx) is used to compute the Electronic Circular Dichroism and absorption spectra of two prototype guanine-rich DNA sequences folded in quadruple helices (GQs), i.e., a fragment of the human telomeric sequence (Tel21, antiparallel), and (TGGGGT)4 (TG4T, parallel). Calculations on different subsets of Tel21 and TG4T, from dimers to tetramers, show that FrDEx provides spectra close to the reference full quantum mechanical (QM) ones (obtained with time-dependent density functional theory), with significant improvements with respect to "standard" excitonic Hamiltonians. Furthermore, these tests enable the most cost-effective procedure for the whole GQ to be determined. FrDEx spectra of Tel21 and TG4T are also in good agreement with the QM and experimental ones and give access to interesting insights into the chemical-physical effects modulating the spectral signals. FrDEx could be profitably used to investigate many other biological and nanotechnological materials, from DNA to (opto)Electronic polymers.
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High‐Resolution Absorption and Electronic Circular Dichroism Spectra of (R)‐(+)‐1‐Phenylethanol. Confident Interpretation Based on the Synergy between Experiments and Computations
Chemphyschem : a European journal of chemical physics and physical chemistry, 2018Co-Authors: Fabrizio Santoro, Farinaz Mortaheb, Jörn Lepelmeier, Ulrich Boesl, Ulrich Heiz, Aras KartouzianAbstract:Using density functional theory and its time-dependent extension for excited states, the S0 →S1 high-resolution vibronic absorption and Electronic Circular Dichroism spectra of (R)-(+)-1-phenylethanol are computed and compared to experimental spectra measured in jet-cooled conditions in the region within 1000 cm-1 of the 0-0 transition. The agreement between theory and computation is satisfactory and allows a confident assignment of several experimental bands in terms of fundamentals of different modes. Cases are documented for which the analysis of optical anisotropy factors, owing to their signed nature, remarkably enhances the possibility of a robust assignment of the experimental absorption bands. Computational analysis shows that the experimental spectra are dominated by Herzberg-Teller contributions and that the Electronic Circular Dichroism spectrum and the anisotropy factors are also strongly modulated by the effect of Duschinsky mixings.
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Vibronic Coupling Explains the Different Shape of Electronic Circular Dichroism and of Circularly Polarized Luminescence Spectra of Hexahelicenes
Journal of chemical theory and computation, 2016Co-Authors: Yanli Liu, Sergio Abbate, Giovanna Longhi, Na Lin, Xian Zhao, Javier Cerezo, Giuseppe Mazzeo, Fabrizio SantoroAbstract:We present the simulation of the absorption (ABS), Electronic Circular Dichroism (ECD), emission (EMI), and Circularly polarized luminescence (CPL) spectra for the weak Electronic transition between the ground (S0) and the lowest excited state (S1) of hexahelicene, 2-methylhexahelicene, 2-bromohexahelicene, and 5-azahexahelicene. Vibronic contributions have been computed at zero Kelvin and at room temperature in harmonic approximation including Duschinsky effects and accounting for both Franck–Condon and Herzberg–Teller contributions. Our results nicely capture the effects of the different substituents on the experimental spectra. They also show that HT effects dominate the shape of ECD and CPL spectra where they even induce changes of signs; HT effects are also relevant in ABS and EMI, tuning the relative intensities of the different vibronic bands. HT effects are the main reason for the differences in the line shapes of ABS and ECD and of EMI and CPL spectra and for the mirror-symmetry breaking between ...
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Vibronic Coupling Dominates the Electronic Circular Dichroism of the Benzene Chromophore 1Lb band
The Journal of organic chemistry, 2013Co-Authors: Gennaro Pescitelli, Lorenzo Di Bari, Antonio Rizzo, Vincenzo Barone, Fabrizio SantoroAbstract:The alkylbenzene derivatives (R)-PhCH(CH3)tBu (1) and (R)-PhCH(CH3)iPr (2) were taken as paradigms of chiral benzene compounds and their vibronic Electronic Circular Dichroism (ECD) spectrum in the 1Lb band region analyzed in detail. The 1Lb ECD band of chiral benzene compounds is often used to assign absolute configurations on the basis of sector rules. However, 1Lb ECD bands of several benzene derivatives are associated with a forbidden character and show marked vibrational progressions strongly modulating their shape. This is also true for compounds 1 and 2, the latter also showing a peculiar thermochromism. The low-temperature ECD spectrum of 2 displays in fact an alternation of positive and negative ECD maxima. Vibronic ECD calculations performed within a TDDFT scheme allowed a full rationalization of the observed ECD spectra of 1 and 2. Especially in the case of 2, the ECD spectrum in the 1Lb band region results from a complex balance of Franck–Condon and Herzberg–Teller effects, as well as of confo...
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Electronic Circular Dichroism in exciton-coupled dimers: vibronic spectra from a general all-coordinates quantum-dynamical approach.
The journal of physical chemistry. A, 2013Co-Authors: Daniele Padula, Gennaro Pescitelli, David Picconi, Alessandro Lami, Fabrizio SantoroAbstract:We present a computational approach of general applicability to simulate the vibronic line shapes of absorption and Electronic Circular Dichroism (ECD) spectra in rigid exciton-coupled dimers based on a time-dependent expression of the spectra and quantum dynamical calculations. We adopt a diabatic model of interacting states localized on the monomers whose Electronic potential energy surfaces are described within harmonic approximation, including the effect of displacements, frequency changes, and normal-mode mixings. Spectra that fully account for the effect of all nuclear degrees of freedom of the system are obtained through a hierarchical representation of the Hamiltonian in blocks, defined so that few blocks accurately describe the short-time dynamics of the system. With this approach, on the ground of time-dependent density functional theory calculations, we simulate the absorption and ECD spectra of a covalent compound representing a “dimer” of anthracene, in the spectral region of the 1La monomer ...
Cecilia Noguez - One of the best experts on this subject based on the ideXlab platform.
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ab initio Electronic Circular Dichroism of fullerenes single walled carbon nanotubes and ligand protected metal nanoparticles
Chirality, 2014Co-Authors: Cecilia Noguez, Francisco J. HidalgoAbstract:The versatility and applicability of a time-perturbed density functional method implemented within the SIESTA program package to calculate Electronic Circular Dichroism of diverse nanoparticles is discussed. Results for nanostructures, such as fullerenes, single-wall carbon nanotubes, as well as metallic nanoparticles composed of up to hundreds of atoms were examined by comparison with previously reported experimental and theoretical results. In all cases, the calculated Electronic Circular Dichroism shows very good consistency with other calculations, and a remarkable agreement with experiments. It is concluded that such a high-level method provides theoretical support for the quantification, understanding, and prediction of chirality and its measurement in nanostructures. It is expected that this information would be useful to motivate further experimental studies and interpretation of optical activity in terms of Electronic Circular Dichroism in novel nanostructures. Chirality 26:553–562, 2014. © 2014 Wiley Periodicals, Inc.
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Ab Initio Electronic Circular Dichroism of Fullerenes, Single‐Walled Carbon Nanotubes, and Ligand‐Protected Metal Nanoparticles
Chirality, 2014Co-Authors: Cecilia Noguez, Francisco J. HidalgoAbstract:The versatility and applicability of a time-perturbed density functional method implemented within the SIESTA program package to calculate Electronic Circular Dichroism of diverse nanoparticles is discussed. Results for nanostructures, such as fullerenes, single-wall carbon nanotubes, as well as metallic nanoparticles composed of up to hundreds of atoms were examined by comparison with previously reported experimental and theoretical results. In all cases, the calculated Electronic Circular Dichroism shows very good consistency with other calculations, and a remarkable agreement with experiments. It is concluded that such a high-level method provides theoretical support for the quantification, understanding, and prediction of chirality and its measurement in nanostructures. It is expected that this information would be useful to motivate further experimental studies and interpretation of optical activity in terms of Electronic Circular Dichroism in novel nanostructures. Chirality 26:553–562, 2014. © 2014 Wiley Periodicals, Inc.