Spectroscopy: Computational Methods

Peyerimhoff, Sigrid D.

doi:10.1002/0470845015.caa010

Cited by 5 publications

(3 citation statements)

References 49 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Nonlinear signals are sensitive to fine details (e.g., anharmonicities, overtone transitions, etc.) and require a high-level Hamiltonian . Vibrational motions and spectra are commonly described by normal modes.…”

Section: Fluctuating Vibrational-exciton Hamiltonianmentioning

confidence: 99%

Simulation Protocols for Coherent Femtosecond Vibrational Spectra of Peptides

et al. 2006

View full text Add to dashboard Cite

Two algorithms for simulating the response of peptides to sequences of IR pulses are developed and applied to N-methyl acetamide (NMA) and a 17 residue alpha-helical peptide (YKKKH17) in D(2)O. A fluctuating vibrational-exciton Hamiltonian for the amide I mode is constructed from molecular dynamics trajectories. Coupling with the environment is described using a density functional theory electrostatic map. The cumulant expansion of Gaussian fluctuation incorporates motional narrowing due to fast frequency fluctuations and is adequate for NMA and for isotopically labeled bands in large peptides. Real-space truncation of the scattering matrix of the nonlinear exciton equations significantly reduces the computational cost, making it particularly attractive for slow fluctuations in large globular proteins.

show abstract

Section: Fluctuating Vibrational-exciton Hamiltonianmentioning

confidence: 99%

Simulation Protocols for Coherent Femtosecond Vibrational Spectra of Peptides

et al. 2006

View full text Add to dashboard Cite

show abstract

“…[40] All electronic structure calculations above were performed using the GAUSSIAN 09 [41] and MOLPRO 2006 [42] program packages.…”

Section: Computational Detailsmentioning

confidence: 99%

Ab initio characterization of size dependence of electronic spectra for linear anionic carbon clusters C_n⁻ (n = 4–17)

2011

View full text Add to dashboard Cite

In this article, we determine the ground-state equilibrium geometries of the linear anionic carbon clusters C n- (n = 4-17) by means of the density functional theory B3LYP, CAM-B3LYP, and coupled cluster CCSD(T) calculations, as well as their electronic spectra obtained by the multireference second-order perturbation theory CASPT2 method. These studies indicate that these linear anions possess doublet ²∏(g) or ²∏(u) ground state, and the even-numbered clusters are generally acetylenic, whereas the odd-numbered ones are essentially cumulenic. The energy differences, electron affinities, and incremental binding energies of C n- chains all exhibit a notable tread of parity alternation, with n-even chains being more stable than n-odd ones. In addition, the predicted vertical excitation energies from the ground state to four low-lying excited states are in reasonably good agreement with the available experimental observations, and the calculations for the higher excited electronic transitions can provide accurate information for the experimentalists and spectroscopists. Interestingly, the absorption wavelengths of the 1²∏(u/g) ← X²∏(g/u) transitions of the n-even clusters show a nonlinear trend of exponential growth, whereas those of the n-odd counterparts are found to obey a linear relationship as a function of the chain size, as shown experimentally. Moreover, the absorption wavelengths of the transitions to the higher excited states of C n- series have the similar linear size dependence as well.

show abstract

“…Kohn–Sham density functional theory (KS-DFT) is now the most widely used method for electronic ground-state calculations of molecules and solids. Because of the moderate computational cost and reasonable accuracy, time-dependent density functional theory (TD-DFT) − based on a KS-DFT reference has become the leading method used to calculate excited-state properties and electronic spectra (see refs − for reviews; for TD-DFT calculations of ground-state properties like dispersion coefficients, see refs and ). It is routinely applicable to large systems (about a few hundred atoms) in which correlated wave-function-based methods of similar accuracy are not feasible.…”

Section: Introductionmentioning

confidence: 99%

Electronic Circular Dichroism of Highly Conjugated π-Systems: Breakdown of the Tamm–Dancoff/Configuration Interaction Singles Approximation

Bannwarth

Grimme

2015

J. Phys. Chem. A

View full text Add to dashboard Cite

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 study the ECD of an α-helix polypeptide chain. Here, the lowest-energy transitions are dominated by localized excitations within the individual peptide units, and TDA methods perform satisfactorily. The results may have far-reaching implications for simple semiempirical methods which often employ TDA and CIS for huge molecules. Our recently presented simplified time-dependent DFT approach proves to be an excellent low-cost linear response method which together with range-separated density functionals like ωB97X-D3 produces ECD spectra in very good agreement with experiment.

show abstract

Spectroscopy: Computational Methods

Cited by 5 publications

References 49 publications

Simulation Protocols for Coherent Femtosecond Vibrational Spectra of Peptides

Simulation Protocols for Coherent Femtosecond Vibrational Spectra of Peptides

Ab initio characterization of size dependence of electronic spectra for linear anionic carbon clusters C_n⁻ (n = 4–17)

Electronic Circular Dichroism of Highly Conjugated π-Systems: Breakdown of the Tamm–Dancoff/Configuration Interaction Singles Approximation

Contact Info

Product

Resources

About

Spectroscopy: Computational Methods

Cited by 5 publications

References 49 publications

Simulation Protocols for Coherent Femtosecond Vibrational Spectra of Peptides

Simulation Protocols for Coherent Femtosecond Vibrational Spectra of Peptides

Ab initio characterization of size dependence of electronic spectra for linear anionic carbon clusters Cn− (n = 4–17)

Electronic Circular Dichroism of Highly Conjugated π-Systems: Breakdown of the Tamm–Dancoff/Configuration Interaction Singles Approximation

Contact Info

Product

Resources

About

Ab initio characterization of size dependence of electronic spectra for linear anionic carbon clusters C_n⁻ (n = 4–17)