Electron density and electrostatic potential-based characteristics of molecular plasmons in polyacenes

2017 ◽  
Author(s):  
Mishu Paul ◽  
Balanarayan Pananghat
Keyword(s):  
Excited States ◽  
Electrostatic Potential ◽  
Ground State ◽  
Density Functional ◽  
Electronic Absorption Spectra ◽  
High Electron ◽  
Excitation Energies ◽  
Electronic Density ◽  
Energy Peak ◽  
Electron Rearrangement

<div>Plasmonic modes in single-molecule systems have been previously identified by scaling two-electron interactions while calculating excitation energies [Bernadotte et al., J. Phys. Chem. C, 2013, <b>117</b>, 1863]. Analysis of transition dipole moments for states of polyacenes based on configuration interaction [Guidez et al., J. Phys. Chem. C, 2013, <b>117</b>, 21466.] was yet another method characterizing molecular plasmons. The principal features in the electronic absorption spectra for polyacenes are a low-intensity, lower-in-energy peak (denoted as α) and a high-intensity, higher-in-energy peak (β ). From our calculations using time-dependent density functional theory (TD-DFT) at B3LYP/cc-pVTZ basis, both the peaks were found to result from the same set of electronic transitions (HOMO-n to LUMO and HOMO to LUMO+n, where n varies as the number of fused rings increases). In this work, the excited states of polyacenes, naphthalene through pentacene, have been analysed using electron densities and molecular electrostatic potential (MESP) topography. The bright and dark plasmonic states involve the least electron rearrangement, as compared to other excited states. Quantitatively, the MESP topography indicates that the variance in MESP values as well as displacement in minima positions (calculated with respect to the ground state) are lowest for plasmonic states. This suggests a resemblance between the plasmonic and ground state electronic density profiles and electrostatic potential topographies. On the other hand, a high electron-rearrangement characterizes a single particle excitation. The molecular plasmon can be called an excited state most similar to the ground state in terms of one-electron properties.</div>

Electron density and electrostatic potential-based characteristics of molecular plasmons in polyacenes

2017 ◽  
Author(s):  
Mishu Paul ◽  
Balanarayan Pananghat
Keyword(s):  
Excited States ◽  
Electrostatic Potential ◽  
Ground State ◽  
Density Functional ◽  
Electronic Absorption Spectra ◽  
High Electron ◽  
Excitation Energies ◽  
Electronic Density ◽  
Energy Peak ◽  
Electron Rearrangement

<div>Plasmonic modes in single-molecule systems have been previously identified by scaling two-electron interactions while calculating excitation energies [Bernadotte et al., J. Phys. Chem. C, 2013, <b>117</b>, 1863]. Analysis of transition dipole moments for states of polyacenes based on configuration interaction [Guidez et al., J. Phys. Chem. C, 2013, <b>117</b>, 21466.] was yet another method characterizing molecular plasmons. The principal features in the electronic absorption spectra for polyacenes are a low-intensity, lower-in-energy peak (denoted as α) and a high-intensity, higher-in-energy peak (β ). From our calculations using time-dependent density functional theory (TD-DFT) at B3LYP/cc-pVTZ basis, both the peaks were found to result from the same set of electronic transitions (HOMO-n to LUMO and HOMO to LUMO+n, where n varies as the number of fused rings increases). In this work, the excited states of polyacenes, naphthalene through pentacene, have been analysed using electron densities and molecular electrostatic potential (MESP) topography. The bright and dark plasmonic states involve the least electron rearrangement, as compared to other excited states. Quantitatively, the MESP topography indicates that the variance in MESP values as well as displacement in minima positions (calculated with respect to the ground state) are lowest for plasmonic states. This suggests a resemblance between the plasmonic and ground state electronic density profiles and electrostatic potential topographies. On the other hand, a high electron-rearrangement characterizes a single particle excitation. The molecular plasmon can be called an excited state most similar to the ground state in terms of one-electron properties.</div>

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.

scholarly journals Equilibrium Geometries, Adiabatic Excitation Energies and Intrinsic C=C/C–H Bond Strengths of Ethylene in Lowest Singlet Excited States Described by TDDFT

Symmetry ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 1545
Author(s):  
Yunwen Tao ◽  
Linyao Zhang ◽  
Wenli Zou ◽  
Elfi Kraka
Keyword(s):  
Excited States ◽  
Ground State ◽  
Density Functional ◽  
Excitation Energies ◽  
Functional Theory ◽  
Local Vibrational Mode ◽  
Strength Change ◽  
Bond Strengths ◽  
First Time ◽  
Equilibrium Geometries

Seventeen singlet excited states of ethylene have been calculated via time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional and the geometries of 11 excited states were optimized successfully. The local vibrational mode theory was employed to examine the intrinsic C=C/C–H bond strengths and their change upon excitation. The natural transition orbital (NTO) analysis was used to further analyze the C=C/C–H bond strength change in excited states versus the ground state. For the first time, three excited states including πy′ → 3s, πy′ → 3py and πy′ → 3pz were identified with stronger C=C ethylene double bonds than in the ground state.

Theoretical studies on ClOO — electronic spectra, ionization potential, and electron affinity

2011 ◽  
Vol 89 (8) ◽  
pp. 891-897 ◽  
Author(s):  
Friedrich Grein
Keyword(s):  
Excited States ◽  
Ground State ◽  
Density Functional ◽  
Oscillator Strengths ◽  
Electron Affinities ◽  
Excitation Energies ◽  
Vertical Excitation ◽  
Avoided Crossings ◽  
Cluster Methods ◽  
Configuration Interaction Calculations

Vertical excitation energies and oscillator strengths of doublet and quartet states of ClOO, covering doublet states up to 7.5 eV and quartet states up to 9 eV, were obtained by multireference configuration interaction calculations. Strong absorptions from the X2A″ ground state are predicted at 186 and 235 nm. Experimentally, a maximum has been found near 248 nm. The grouping of excited states, with twelve low-lying doublet states and three low-lying quartet states, is explained by the interaction of the 2P ground state of Cl with the π*2 states 3Σg–, 1Δg, and 1Σg+ of O2. Potential energy curves for Cl–O separation at fixed O–O distance and ClOO angle show the lower states to be repulsive (with the exception of the ground state), and higher states to have minima due to avoided crossings. The lowest Rydberg states are expected around 8.5 eV. Adiabatic ionization potentials (IP) and electron affinities (EA) of ClOO were obtained by density functional and coupled cluster methods, with values of 11.60–11.79 eV for IP and 3.56–3.79 eV for EA.

scholarly journals Exploitation of Baird Aromaticity and Clar’s Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons

Chemistry ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 532-549
Author(s):  
Felix Plasser
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Excited States ◽  
Aromatic Hydrocarbons ◽  
Density Functional ◽  
Materials Science ◽  
Chemical Shifts ◽  
Qualitative Description ◽  
Triplet States ◽  
Excitation Energies ◽  
Polycyclic Aromatic

Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four biphenylene-derived PAHs finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). The results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states.

Multiconfiguration pair-density functional theory for doublet excitation energies and excited state geometries: the excited states of CN

2017 ◽  
Vol 19 (44) ◽  
pp. 30089-30096 ◽  
Author(s):  
Jie J. Bao ◽  
Laura Gagliardi ◽  
Donald G. Truhlar
Keyword(s):  
Density Functional Theory ◽  
Excited State ◽  
Excited States ◽  
Density Functional ◽  
Excitation Energies ◽  
Functional Theory ◽  
Pair Density

MC-PDFT is more accurate than CR-EOM-CCSD(T) or TDDFT when averaged over the first four adiabatic excitation energies of CN.

scholarly journals Exploitation of Baird Aromaticity and Clar's Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons

2021 ◽  
Author(s):  
Felix Plasser
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Excited States ◽  
Aromatic Hydrocarbons ◽  
Density Functional ◽  
Materials Science ◽  
Chemical Shifts ◽  
Qualitative Description ◽  
Triplet States ◽  
Excitation Energies ◽  
Polycyclic Aromatic

Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four PAHs based on the biphenylene motif finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). These results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states.

The ground state and low-lying excited states of CCCN radical and its ions: a CASSCF/CASPT2 study

2016 ◽  
Vol 94 (9) ◽  
pp. 803-807
Author(s):  
Angyang Yu
Keyword(s):  
Excited States ◽  
Ground State ◽  
Linear Structure ◽  
Electronic Configuration ◽  
Geometric Optimization ◽  
Oscillator Strengths ◽  
Basis Set ◽  
Excitation Energies ◽  
Complete Active Space ◽  
Vertical Excitation

The ground state and low-lying excited states of the CCCN radical and its ions have been investigated systematically using the complete active space self-consistent field (CASSCF) and multi-configuration second-order perturbation theory (CASPT2) methods in conjunction with the ANO-RCC-TZP basis set. The calculated results show that the state 12Σ+ has the lowest CASPT2 energy among the electronic states. By means of the geometric optimization of this radical, it could be found that the molecule exhibits linear structure, with the bond lengths R1 = 1.214 Å, R2 = 1.363 Å, R3 = 1.162 Å, which are very close to the experimental values. The calculated vertical excitation energies and the corresponding oscillator strengths show that there are three relatively strong peaks at energies 0.63, 4.04, and 5.49 eV, which correspond to the transitions 12Σ+ → 12Π, 12Σ+ → 22Π, and 12Σ+ → 22Σ+, respectively. Additionally, the electronic configuration and the harmonic vibration frequencies of each state are also investigated.

INVESTIGATION OF DOMINANT ELECTRON CONFIGURATIONS IN TIME-DEPENDENT DENSITY FUNCTIONAL THEORY

2005 ◽  
Vol 04 (01) ◽  
pp. 265-280 ◽  
Author(s):  
SUSUMU YANAGISAWA ◽  
TAKAO TSUNEDA ◽  
KIMIHIKO HIRAO
Keyword(s):  
Density Functional Theory ◽  
Small Molecules ◽  
Excited States ◽  
Density Functional ◽  
Time Dependent ◽  
Response Matrix ◽  
Excitation Energies ◽  
Functional Theory ◽  
Electron Transitions ◽  
Dependent Density

We investigated the electron configurations that are dominant in excited states of molecules in time-dependent density functional theory (TDDFT). By taking advantage of the discussion on off-diagonal elements in the TDDFT response matrix (Appel et al., Phys Rev Lett, 90, 043005, 2003), we can pick up electron transitions that contribute to an excitation of interest by making use of the diagonal elements of the TDDFT matrix. We can obtain approximate excitation energies by calculating a TDDFT submatrix, which is contracted for a list of collected transitions. This contracted TDDFT was applied to the calculation of excitation energies of the CO molecule adsorbing Pt 10 cluster and some prototype small molecules. Calculated results showed that a TDDFT excitation energy is dominated by a few electron configurations, unless severe degeneracy is involved.

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