scholarly journals The 6.2 μm PAH Feature and the Role of Nitrogen: Revisited

2021 ◽  
Vol 923 (2) ◽  
pp. 202
Author(s):  
A. Ricca ◽  
C. Boersma ◽  
E. Peeters
Keyword(s):  
Density Functional ◽  
Molecular Geometry ◽  
Peak Position ◽  
Basis Sets ◽  
Functional Theory ◽  
Class A ◽  
Band Position ◽  
Polycyclic Aromatic ◽  
Map Data

Abstract This study revisits the role that nitrogen inclusion in polycyclic aromatic hydrocarbons (PAHs; those with nitrogen inclusion, PANHs) plays in their infrared (IR) spectral properties. We present spectra of pure PAHs, PANHs, and protonated PANHs, computed using density functional theory and basis sets that treat polarization. We investigate trends in peak position and relative intensities as a function of nitrogen position, charge, and geometry. We use Spitzer-IRS spectral map data of the northwest photodissociation region of NGC 7023 and a database-fitting approach, using exclusively the PA(N)H spectra computed in this paper, to assess their IR contribution to the cosmic PAH emission. We find that, by including the treatment of polarization, pure PAH cations can account for the class A 6.2 μm PAH emission, with the 6.2 μm band position being dependent on the molecular geometry. PANH cations are required to reproduce the most blueshifted 6.2 μm bands observed in class A sources, albeit PANH cations come with strong 11.0 μm emission. Blind database fits demonstrate that the restriction imposed by the 11.0 μm emission in the astronomical spectra limits the contribution of PANH cations and the fits have to use neutral PANHs to avoid inflating the 11.0 μm feature even further. By assuming that all of the 11.0 μm emission is due to PANHs, we derive an upper limit for the contribution of PANH cations to the astronomical 6.2 μm PAH band of ∼12%. The fits further show hydrogenated PANHs significantly contributing in NGC 7023's more benign region, supporting the view that shielded environments could sustain protonated PA(N)Hs.

Comparison of different theory models and basis sets for the calculation of FbC-M10Iso-Bn geometry and geometries of chlorin-imide and chlorin-isoimide isomeric pairs

2013 ◽  
Vol 17 (05) ◽  
pp. 376-383 ◽  
Author(s):  
Jong-Kil Park ◽  
Sang Joon Choe
Keyword(s):  
Density Functional ◽  
Molecular Geometry ◽  
Basis Sets ◽  
Normal Coordinate ◽  
Dft Methods ◽  
Functional Theory ◽  
X Ray ◽  
Bond Lengths ◽  
X Ray Crystallography ◽  
Isomeric Pairs

Various density functional theory (DFT) methods with different basis sets to predict the molecular geometry of FbC-M10Iso-Bn macrocycle, a chlorin-isoimide, are compared in this study. DFT methods, including M06-2X, B3LYP, LSDA, B3PW91, PBEPBE, and BPV86, are examined. Different basis sets, such as 6-31G*, 6-31+G (d, p), 6-311+G (d, p), 6-311++G (d, p), cc-PVDZ, cc-PVTZ, and cc-PVQZ are also considered. The examined hybrid DFT methods are in agreement with the geometry of X-ray crystallography available for comparison. B3LYP/cc-PVDZ level is particularly consistent with available X-ray crystallography in terms of predicting the geometries of FbC-M10Iso-Bn. Geometries of chlorin-imide and chlorin-isoimide isomeric pairs are described through B3LYP/cc-PVDZ method. The bond lengths of chlorin-isoimide, specifically C13–C14, C14–C15, and C2–C3, increase as bond overlap index decreases because of charge transfer. β-β bond lengths (C2–C3 bond lengths) with a three-substituent benzylcarbamoyl group also increase as bond overlap index decreases compared with other molecules. The bond lengths of chlorin-imide are smaller than those of chlorin-isoimide. Angles with β-β bond lengths, specifically C2–C3–C4 in ring A, also decrease with a three-substituent benzylcarbamoyl group; however, the angles in C1–C2–C3 increase. Potential energy on the surfaces of the chlorin-imide and chlorin-isoimide isomeric pairs is optimized by calculating the total and relative energies at B3LYP/cc-PVDZ level. Results indicate that chlorin-imides are more stable than chlorin-isoimides. Normal-coordinate structural decomposition shows that chlorin-imides exhibit greater deformation than chlorin-isoimides except for FbC-M10Iso-Ph.

scholarly journals Aromatic adsorption on metals via first-principles density functional theory

2009 ◽  
Vol 465 (2110) ◽  
pp. 2949-2976 ◽  
Author(s):  
S. J. Jenkins
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Functional Theory ◽  
Aromatic Molecules ◽  
Polycyclic Aromatic ◽  
Non Covalent Interactions ◽  
Covalent Interactions ◽  
Case Basis ◽  
Electronic And Steric Effects

We review first-principles calculations relevant to the adsorption of aromatic molecules on metal surfaces. Benzene has been intensively studied on a variety of substrates, providing an opportunity to comment upon trends from one metal to another. Meanwhile, calculations elucidating the adsorption of polycyclic aromatic molecules are more sparse, but nevertheless yield important insights into the role of non-covalent interactions. Heterocyclic and substituted aromatic compounds introduce the complicating possibility of electronic and steric effects, whose relative importance can thus far only be gauged on a case-by-case basis. Finally, the coadsorption and/or reaction of aromatic molecules is discussed, highlighting an area where the predictive power of theory is likely to prove decisive in the future.

Role of Augmented Basis Sets and Quest for ab Initio Performance/Cost Alternative to Kohn–Sham Density Functional Theory

2019 ◽  
Vol 124 (1) ◽  
pp. 126-134 ◽  
Author(s):  
Marco Martínez González ◽  
F. George D. Xavier ◽  
Jing Li ◽  
Luis A. Montero-Cabrera ◽  
Jose M. Garcia de la Vega ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Basis Sets ◽  
Functional Theory

The Nature of S-N Bonding in Sulfonamides and Related Compounds: Insights into π-Bonding Contributions from Sulfur K-Edge XAS

2020 ◽  
Author(s):  
Tulin Okbinoglu ◽  
Pierre Kennepohl
Keyword(s):  
Density Functional ◽  
Chemical Properties ◽  
Functional Theory ◽  
Rotational Barriers ◽  
Td Dft ◽  
Nitrogen Bonds ◽  
X Ray Absorption ◽  
Related Compounds ◽  
And Chemical Properties

Molecules containing sulfur-nitrogen bonds, like sulfonamides, have long been of interest due to their many uses and chemical properties. Understanding the factors that cause sulfonamide reactivity is important, yet their continues to be controversy regarding the relevance of S-N π bonding in describing these species. In this paper, we use sulfur K-edge x-ray absorption spectroscopy (XAS) in conjunction with density functional theory (DFT) to explore the role of S<sub>3p</sub> contributions to π-bonding in sulfonamides, sulfinamides and sulfenamides. We explore the nature of electron distribution of the sulfur atom and its nearest neighbors and extend the scope to explore the effects on rotational barriers along the sulfur-nitrogen axis. The experimental XAS data together with TD-DFT calculations confirm that sulfonamides, and the other sulfinated amides in this series, have essentially no S-N π bonding involving S<sub>3p</sub> contributions and that electron repulsion and is the dominant force that affect rotational barriers.

Benchmark of Simplified Time-Dependent Density Functional Theory for UV-Vis Spectral Properties of Porphyrinoids

2019 ◽  
Author(s):  
Kamal Batra ◽  
Stefan Zahn ◽  
Thomas Heine
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Large Scale ◽  
Absolute Error ◽  
Time Dependent ◽  
Basis Set ◽  
Basis Sets ◽  
Functional Theory ◽  
Framework Materials ◽  
Dependent Density

<p>We thoroughly benchmark time-dependent density- functional theory for the predictive calculation of UV/Vis spectra of porphyrin derivatives. With the aim to provide an approach that is computationally feasible for large-scale applications such as biological systems or molecular framework materials, albeit performing with high accuracy for the Q-bands, we compare the results given by various computational protocols, including basis sets, density-functionals (including gradient corrected local functionals, hybrids, double hybrids and range-separated functionals), and various variants of time-dependent density-functional theory, including the simplified Tamm-Dancoff approximation. An excellent choice for these calculations is the range-separated functional CAM-B3LYP in combination with the simplified Tamm-Dancoff approximation and a basis set of double-ζ quality def2-SVP (mean absolute error [MAE] of ~0.05 eV). This is not surpassed by more expensive approaches, not even by double hybrid functionals, and solely systematic excitation energy scaling slightly improves the results (MAE ~0.04 eV). </p>

γ-Valerolactone-Introduced Controlled-Isomerization of Glucose for Lactic Acid Production over Sn-Beta Catalyst

2021 ◽  
Author(s):  
Xinpeng Zhao ◽  
Zhimin Zhou ◽  
hu luo ◽  
Yanfei Zhang ◽  
Wang Liu ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Lactic Acid ◽  
Dft Calculations ◽  
Acid Production ◽  
Density Functional ◽  
Lactic Acid Production ◽  
Hydrothermal Conversion ◽  
Functional Theory ◽  
Environment Friendly

Combined experiments and density functional theory (DFT) calculations provided insights into the role of the environment-friendly γ-valerolactone (GVL) as a solvent in the hydrothermal conversion of glucose into lactic acid...

scholarly journals Role of Chemistry and Crystal Structure on the Electronic Defect States in Cs-Based Halide Perovskites

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1032
Author(s):  
Anirban Naskar ◽  
Rabi Khanal ◽  
Samrat Choudhury
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Covalent Bond ◽  
Density Functional Theory Calculations ◽  
Antisite Defect ◽  
Defect States ◽  
Functional Theory ◽  
Electronic Defect ◽  
Constituent Elements

The electronic structure of a series perovskites ABX3 (A = Cs; B = Ca, Sr, and Ba; X = F, Cl, Br, and I) in the presence and absence of antisite defect XB were systematically investigated based on density-functional-theory calculations. Both cubic and orthorhombic perovskites were considered. It was observed that for certain perovskite compositions and crystal structure, presence of antisite point defect leads to the formation of electronic defect state(s) within the band gap. We showed that both the type of electronic defect states and their individual energy level location within the bandgap can be predicted based on easily available intrinsic properties of the constituent elements, such as the bond-dissociation energy of the B–X and X–X bond, the X–X covalent bond length, and the atomic size of halide (X) as well as structural characteristic such as B–X–B bond angle. Overall, this work provides a science-based generic principle to design the electronic states within the band structure in Cs-based perovskites in presence of point defects such as antisite defect.

Sign in / Sign up

Export Citation Format

Share Document