Optical Absorption Spectra of V⁺₄ Isomers: One Example of First-Principles Theoretical Spectroscopy with Time-Dependent Density Functional Theory

Abstract

The optical absorption spectrum of the three most stable isomers of the Ag11 system was calculated using the time-dependent density functional theory, with the generalized gradient approximation for the exchange and correlation potential, and a relativistic pseudopotential parametrization for the modelling of the ion-electron interaction. The computational scheme is based on a real space code, where the photoabsorption spectrum is calculated by using the formalism developed by Casida. The significantly different spectra of the three isomers permit the identification of the ground-state configuration predominantly present in the laboratory beams in base to a comparison between the calculated photoabsorption spectrum of the most stable configuration of Ag11 and the measured spectra of medium-size silver clusters trapped in noble gas Ar and Ne matrices at different temperatures. This assignment is confirmed by the fact that this isomer has the lowest calculated energy.

Effect of van der Waals forces on the stacking of coronenes encapsulated in a single-wall carbon nanotube and many-body excitation spectrum

“…A method extensively used to calculate the photoabsorption spectrum of nanostructures, surfaces and solids is the time-dependent density functional theory [41,42] (TDDFT), which states a good performance for low electronically correlated systems through the time-evolution of the Kohn-Sham states. Nevertheless, as previously indicated, the implementations used in practice have some well-known limitations due to the approximate description of exchange and correlation effects between the electrons.…”

“…The finite width of the excitation peaks in an experimental spectrum -linked to the accessible resolution -is mostly determined by the temperature. In our calculations, on the other hand, each excitation peak in the spectrum has been broadened by a Lorentzian profile, where the broadening parameter η is set equal to 0.2 eV, a value commonly used in order to mimic the experimental resolution [42].…”

Electronic and atomic structure of the AlnHn+2 clusters

“…In addition, Koponen et al 33 concluded that the LDA performs much better in the TDDFT, compared to static DFT. On the other hand, the most important requirement in obtaining a good photoabsorption spectrum is to have accurate single-particle energies and orbitals, obtained with a good static XC potential, 34,35 while the kernel is less important. The paper by Castro et al 19 presents a discussion of the influence of different XC kernels in the calculation of the optical spectrum of clusters by TDDFT.…”

“…In this equation ⑀ represents the energy, the ⑀ i are the discrete excitation energies obtained by the Casida method, 31,32 and the value of the parameter A determines the full width at half maximum, set in this work equal to 0.05 eV, which is a value commonly used 34 in order to simulate the available resolution in experiments of photoabsorption and photodissociative spectroscopy. This formalism has provided successful results in the calculation of the photoabsorption spectra of atoms, and different types of clusters, [34][35][36][37][38][39] even at high excitation energies. 35 Figure 7 shows the calculated photoabsorption cross sections of the neutral Al n H n+2 and anionic Al n H n+2 − clusters for excitation energies up to 12 eV.…”

Substituent and Solvent Effects on the Absorption Spectra of Cation−π Complexes of Benzene and Borazine: A Theoretical Study

“…Time-dependent density functional theory (TDDFT) found wide application in chemistry and applied physics for calculating the electronic excitations of smaller and larger molecules. , This type of calculation has been well-implemented using the polarized continuum model (PCM) to understand the phenomenon of solvatochomism in various organic and organometallic systems. , Hence, relying on the TDDFT method, we have implemented this method to evaluate the ground-state electronic transitions of various alkali metal (Li + , Na + , and K + ) cation−π complexes of benzene and borazine. We have considered cation−π complexes of benzene and borazine having different substituents at 1, 3, 5 position of benzene and at the boron atoms in borazine (Scheme ).…”