Density functional calculations of excitation energies and oscillator strengths for and excitations and ionization potentials in carbonyl containing molecules

1995 ◽  
Vol 191 (1-3) ◽  
pp. 141-154 ◽  
Author(s):  
M. Stener ◽  
A. Lisini ◽  
P. Decleva
Keyword(s):  
Density Functional Calculations ◽  
Density Functional ◽  
Ionization Potentials ◽  
Oscillator Strengths ◽  
Excitation Energies

scholarly journals Unraveling the Effects of Co-Crystallization on the UV/Vis Absorption Spectra of an N-Salicylideneaniline Derivative. A Computational RI-CC2 Investigation

Molecules ◽  
2020 ◽  
Vol 25 (19) ◽  
pp. 4512
Author(s):  
Jean Quertinmont ◽  
Tom Leyssens ◽  
Johan Wouters ◽  
Benoît Champagne
Keyword(s):  
Optical Properties ◽  
Crystal Field ◽  
Indirect Effects ◽  
Density Functional ◽  
Crystal Packing ◽  
Density Functional Theory Method ◽  
Oscillator Strengths ◽  
Excitation Energies ◽  
Keto Form ◽  
Cell Parameters

This work aims at unraveling the effects of co-crystallization on the optical properties of an N-salicylideneaniline-derived molecular switch transforming between an enol and a keto form. This is achieved by way of a two-step multi-scale method where (i) the molecular geometry and unit cell parameters are optimized using a periodic boundary conditions density functional theory method and (ii) the optical properties are computed for a selection of clusters embedded in an array of point-charges that reproduce the crystal field electronic potential. The optical properties (vertical excitation energies and oscillator strengths) are obtained at the RI-CC2/def2-TZVPD level of approximation. This method allows us to decompose the effects of co-crystallization into (i) indirect effects, the geometry changes of the chromophore due to crystal packing with the coformer, and (ii) direct ones, the polarization due to the interacting coformer and to the crystal field. For the former effects, variations of a crucial torsion angle lead to modification of the π-conjugation and therefore to the decrease or increase of the excitation energies. About the latter, they are antagonistic: (i) the coformer is not directly involved in the excitations but its polarization decreases the excitation energies while (ii) the crystal field has the opposite effect. For the co-crystals with succinic and fumaric acids, combining these direct and indirect effects leads to a hypsochromic shift of the first absorption band with respect to the reference crystal, in agreement with experimental data.

Geometry Optimization, UV/Vis, NBO, HOMO and LUMO, Excited State and Antioxidant Evaluation of Pyrimidine Derivatives

2020 ◽  
Vol 17 ◽  
Author(s):  
Siyamak Shahab ◽  
Masoome Sheikhi ◽  
Evgeni Kvasyuk ◽  
Aliaksei G. Sysa ◽  
Radwan Alnajjar ◽  
...  
Keyword(s):  
Density Functional ◽  
Antioxidant Properties ◽  
Geometry Optimization ◽  
Dft Method ◽  
Oscillator Strengths ◽  
Equilibrium Geometry ◽  
Pyrimidine Derivatives ◽  
Excitation Energies ◽  
Solvent Water ◽  
Homo And Lumo

: In this research, the four pyrimidine derivatives have been studied by using density functional theory (DFT/B3LYP/6-31G*) in solvent water for the first time. After quantum-chemical calculations, the title compounds have been synthesized. The electronic spectra of the new derivatives in a solvent water were performed by time-dependent DFT (TD-DFT) method. The equilibrium geometry, the HOMO and LUMO orbitals, MEP, excitation energies, natural charges, oscillator strengths for the molecules have also been calculated. NBO analysis has been calculated in order to elucidate the intramolecular, rehybridization and delocalization of electron density. These molecules have high antioxidant potential due to the planarity and formation of intramolecular hydrogen bonds. Antioxidant properties of the title compounds have been investigated and discussed.

scholarly journals OS100: A Benchmark Set of 100 Digitized UV-Visible Spectra and Derived Experimental Oscillator Strengths

2021 ◽  
Author(s):  
Astrid Tarleton ◽  
Jorge Garcia-Alvarez ◽  
Anah Wynn ◽  
Cade Awbrey ◽  
Tomas Roberts ◽  
...  
Keyword(s):  
Density Functional ◽  
Oscillator Strengths ◽  
Learning Approaches ◽  
Excitation Energies ◽  
Absorption Bands ◽  
Visible Absorption ◽  
Plain Text ◽  
Solvent Model ◽  
Visible Spectra ◽  
Uv Visible

Excited-state quantum chemical calculations typically report excitation energies and oscillator strengths, ƒ, for each electronic transition. On the other hand, UV-visible spectrophotometric experiments report energy-dependent molar extinction/attenuation coefficients, ε(v), that determine the absorption band line shapes. ε(v) and ƒ are related, but this relation is complicated by various broadening and solvation effects. We fit and integrated experimental UV-visible spectra to obtain ƒexp values for absorption bands and estimated the uncertainty in the fitting. We derived 164 ƒexp values from 100 organic molecules ranging in size from 6-34 atoms. The corresponding computed oscillator strengths (ƒcomp) were obtained with time-dependent density functional theory and a polarizable continuum solvent model. By expressing experimental and computed absorption strengths using a common quantity, we directly compared ƒcomp and ƒexp. While ƒcomp and ƒexp are well correlated (linear regression R2=0. 921), ƒcomp in most cases significantly overestimates ƒexp (regression slope=1.34). The agreement between absolute ƒcomp and ƒexp values was substantially improved by accounting for a solvent refractive index factor, as suggested in some derivations in the literature. The 100 digitized UV-visible spectra are included as plain text files in the supporting information to aid in benchmarking computational or machine-learning approaches that aim to simulate realistic UV-visible absorption spectra.

DFT/MRCI calculations on the excited states of porphyrin, hydroporphyrins, tetrazaporphyrins and metalloporphyrins

2001 ◽  
Vol 05 (03) ◽  
pp. 225-232 ◽  
Author(s):  
ANDREAS B. J. PARUSEL ◽  
STEFAN GRIMME
Keyword(s):  
Excited States ◽  
Density Functional ◽  
Significant Contribution ◽  
Electronic Absorption Spectra ◽  
Blue Shift ◽  
Oscillator Strengths ◽  
Excitation Energies ◽  
Functional Theory ◽  
Intense Color ◽  
Higher Excited States

A combination of density functional theory and multi-reference configuration interaction methods (DFT/MRCI) has been applied to the calculation of electronic absorption spectra in a series of porphyrin-type molecules. The calculated excitation energies and oscillator strengths for free-base porphyrin ( PH 2) are in excellent agreement with experiment for both lower and higher excited states which are characterized by a significant contribution of double excitations (>20%). The 41 B 2 u , 41 B 3 u , and 51 B 2 u states are assigned to the L-band and the 71 B 3 u state to the M-band. The results for the hydroporphyrins chlorin ( CH 2) and bacteriochlorin ( BH 2) are in agreement with the experimentally observed increase in intensity for the Q-bands relative to PH 2. For BH 2 we predict a red shift of the Q x -band (0.2 eV) and a blue shift of the B-band (0.5–0.7 eV) in comparison to both PH 2 and CH 2. For porphyrazine ( PzH 2) and the commercial pigment phthalocyanine ( PcH 2) the calculated oscillator strengths of the Q- and B-bands are of comparable size explaining the intense color of PcH 2. For the metalloporphyrins with magnesium ( PMg ) and zinc ( PZn ), the x- and y-polarized components of the Q- and B-bands collapse, due to the higher D4 h symmetry of the molecules. The calculations reproduce the slight, experimentally observed increase in the oscillator strength of the Q-band and the decrease for the B-band. These effects are ascribed to the electropositive nature of the metals relative to hydrogen. Except for the Q-bands, which are adequately described by the 'four-orbital model,' it is essential to account for excitations outside the four frontier orbitals as well as double and triple excitations for accurate reproduction of experimental data. We compare our results both with experiment and, where available, recent first-principle SAC-CI, MRMP, and TDDFT calculations.

Sign in / Sign up

Export Citation Format

Share Document