Experimental and Theoretical Studies of Rotational Barriers in Aceto-, N-Methylaceto- and N-Phenylacetohydroxamic Acid

2001 ◽  
Vol 66 (1) ◽  
pp. 99-108 ◽  
Author(s):  
David A. Brown ◽  
Laurence P. Cuffe ◽  
Geraldine M. Fitzpatrick ◽  
Noel J. Fitzpatrick ◽  
William K. Glass ◽  
...  
Keyword(s):  
Gas Phase ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Zero Point ◽  
Density Functional Theory Calculations ◽  
Point Energy ◽  
Hartree Fock ◽  
Barrier Heights ◽  
Rotational Barriers ◽  
Moller Plesset

Experimental and theoretical calculations for the E and Z forms of aceto-, N-methylaceto- and N-phenylacetohydroxamic acid are reported. The experimental method was NMR spectroscopy, while the computational methods included Hartree-Fock, Møller-Plesset and density functional theory calculations, with and without solvation, using either the Onsager or Tomasi's PCM method. In all calculations zero point energy corrections were included. The computed results when compared with the experimental ones show that, irrespective of the method used, the differences in the rotational barriers, ∆(E-TS) and ∆(Z-TS), are slight and below the 3 kcal mol-1 limit of the theoretical methods. In general the results using the PCM method were worse than the ones obtained from gas phase calculations or using the Onsager method, even though the PCM method is computationally most expensive. The calculations show, using either the Hartree-Fock or the B3LYP approach, that considering solvation using the Onsager method improves agreement with the experiment results. The calculated barrier heights, excluding the PCM method, agree broadly with the experimental results. Thus using the Onsager approach or gas phase calculations adequate results for barrier heights, but not for relative differences, were obtained.

First–Principles Study Including Zero Point Energy on Hydrogen in Palladium for Hydrogen Membranes Applications

2014 ◽  
Vol 875-877 ◽  
pp. 635-641
Author(s):  
Ali Marashdeh
Keyword(s):  
Bulk Modulus ◽  
Density Functional ◽  
Direct Method ◽  
Harmonic Approximation ◽  
Zero Point ◽  
Density Functional Theory Calculations ◽  
Generalized Gradient ◽  
Zero Point Energy ◽  
Point Energy ◽  
Metal Lattice

Density functional theory calculations at the generalized gradient approximation level are performed on cube clusters that comprise both the metal lattice (Pd) and the interstitial lattice (H). The calculations consider H on the octahedral sites of the metal lattice, i.e., cubes structures Pd4H4-x(x=0–4). For each structure, the cell volume, the total energy, the bulk modulus and the derivative of the bulk modulus have been calculated. Zero point energy (ZPE) corrections have been included using the direct method. The calculations confirm that including ZPE effects in the harmonic approximation has a significant effect on the calculated properties by increasing the cell-volumes and decreasing the bulk modulus. The absorption energies of hydrogen in palladium without including ZPE are found to be exothermic processes. When the ZPE is included, adding the first three Hs atom are exothermic processes while the fourth atom is found to be endothermic.

scholarly journals Quantum-Induced Symmetry-Breaking in the Deuterated Dihydroanthracenyl Radical

2019 ◽  
Author(s):  
Olha Krechkivska ◽  
Callan Wilcox ◽  
Klaas Nauta ◽  
Scott Kable ◽  
Timothy Schmidt
Keyword(s):  
Symmetry Breaking ◽  
Density Functional ◽  
Low Frequency ◽  
Zero Point ◽  
Density Functional Theory Calculations ◽  
Spectral Lines ◽  
Point Energy ◽  
Flight Mass Spectrometry ◽  
Deuterated Analogue ◽  
Vibrational Progression

The hydrogen-atom adduct with anthracene, 9-dihydroanthracenyl radical (C<sub>14</sub>H<sub>11</sub>), and its deuterated analogue, have been identified by laser spectroscopy coupled to time-of-flight mass spectrometry, supported by time-dependent density functional theory calculations. The electronic spectrum of 9-dihydroanthracenyl radical exhibits an origin band at 19115 cm<sup>-1</sup> and its ionization energy was determined to be 6.346(1) eV. The spectra reveal a low-frequency vibrational progression corresponding to a mode described by a butterfly-inversion. In the deuterated analogue, a zero-point-energy imbalance along this coordinate is found to lead to a doubling of the observed spectral lines in the progression. This is attributed to quantum-induced symmetry breaking as previously observed in isotopologues of CH<sub>5</sub><sup>+</sup>.

Quantum-Induced Symmetry-Breaking in the Deuterated Dihydroanthracenyl Radical

2019 ◽  
Author(s):  
Olha Krechkivska ◽  
Callan Wilcox ◽  
Klaas Nauta ◽  
Scott Kable ◽  
Timothy Schmidt
Keyword(s):  
Symmetry Breaking ◽  
Density Functional ◽  
Low Frequency ◽  
Zero Point ◽  
Density Functional Theory Calculations ◽  
Spectral Lines ◽  
Point Energy ◽  
Flight Mass Spectrometry ◽  
Deuterated Analogue ◽  
Vibrational Progression

The hydrogen-atom adduct with anthracene, 9-dihydroanthracenyl radical (C<sub>14</sub>H<sub>11</sub>), and its deuterated analogue, have been identified by laser spectroscopy coupled to time-of-flight mass spectrometry, supported by time-dependent density functional theory calculations. The electronic spectrum of 9-dihydroanthracenyl radical exhibits an origin band at 19115 cm<sup>-1</sup> and its ionization energy was determined to be 6.346(1) eV. The spectra reveal a low-frequency vibrational progression corresponding to a mode described by a butterfly-inversion. In the deuterated analogue, a zero-point-energy imbalance along this coordinate is found to lead to a doubling of the observed spectral lines in the progression. This is attributed to quantum-induced symmetry breaking as previously observed in isotopologues of CH<sub>5</sub><sup>+</sup>.

scholarly journals Theoretical Calculations for the Acidity of Cyanopolyynes HC2n+1N (n = 0–5) in Gas and Aqueous Phases Using Ab initio Methods

2019 ◽  
Vol 7 (1) ◽  
pp. 27
Author(s):  
Hassan H. Abdallah
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Dust Cloud ◽  
Basis Set ◽  
Ab Initio Methods ◽  
Functional Theory ◽  
Moller Plesset ◽  
Cold Dust

Cyanopolyynes have been found in the interstellar medium, cold dust cloud Taurus Molecular Cloud-1, and the Titan’s atmosphere. Theoretical calculations are carried out to predict gas and aqueous phase acidities of a series of cyanopolyynes acids. Two levels of theory were used in this study, with the combination of density functional theory, and Møller–Plesset perturbation (MP2) theory, MP2 methods with two types of basis set, namely, Pople’s 6–311++g (d, p) basis set and Dunning’s aug-cc-pVTZ basis set. The calculations of these molecules reveal that pKa values varying from 12.25 to 17.25 and indicate that the acidity of these molecules in aqueous phase increases whereas the acidity in gas phase decreases with an increasing chain length of these acids.

Polaronic and Bipolaronic Enhancement of Second Hyperpolarizabilities in Dithienyl Polyenes from Ab Initio Quantum Methods

1999 ◽  
Vol 597 ◽  
Author(s):  
Steven Trohalaki ◽  
Robert J. Zellmer ◽  
Ruth Pachter
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Valence Bond ◽  
Closed Shell ◽  
Functional Theory ◽  
Molecular Conformations ◽  
Hartree Fock ◽  
Molecular Charge ◽  
Field Methodology ◽  
Moller Plesset

AbstractSpangler and He [1,2] have shown that dithienyl polyenes form extremely stable bipolaronic dications when oxidatively doped in solution. Previous theoretical studies applied empirical methods to predict bipolaronic enhancement of hyperpolarizabilities for simple polyenes [3,4]. Here, we employ density functional theory to optimize the gas-phase molecular conformations of neutral, cationic, and dicationic forms of a series of dithienyl polyenes, where the number of ethene units, N, is varied from 1–5. Ab initio Hartree-Fock, generalized valence bond, configuration interaction, and Møller-Plesset calculations demonstrate that the dications are farily well described with a closed shell and therefore have little biradicaloid character. Second hyperpolarizabilities, γ, are subsequently calculated using ab initio Hartree-Fock theory and a finite field methodology. As expected, γ increases with the number of ethene units for a given molecular charge. The cations also show the largest increase in γ with N. For a given value of N, the cations display the largest γ values. However, if we treat the dication as a triplet, which might be present in solution, then it displays the largest γ.

scholarly journals Effect of Hartree–Fock pseudopotentials on local density functional theory calculations

2018 ◽  
Vol 20 (27) ◽  
pp. 18844-18849 ◽  
Author(s):  
Hengxin Tan ◽  
Yuanchang Li ◽  
S. B. Zhang ◽  
Wenhui Duan
Keyword(s):  
Density Functional Theory ◽  
Band Gap ◽  
Density Functional ◽  
Local Density ◽  
Density Functional Theory Calculations ◽  
Optimal Choice ◽  
Functional Theory ◽  
Hartree Fock ◽  
Local Density Functional Theory ◽  
Local Density Functional

Optimal choice of the element-specific pseudopotential improves the band gap.

scholarly journals Vibrationally and Spin-Orbit-Resolved Inner-Shell X-ray Absorption Spectroscopy of the NH+ Molecular Ion: Measurements and ab Initio Calculations

Atoms ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 67
Author(s):  
Stéphane Carniato ◽  
Jean-Marc Bizau ◽  
Denis Cubaynes ◽  
Eugene T. Kennedy ◽  
Ségolène Guilbaud ◽  
...  
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Theoretical Calculations ◽  
High Sensitivity ◽  
Open Shell ◽  
Field Configuration ◽  
High Spectral Resolution ◽  
Spin Orbit ◽  
Molecular Ion ◽  
Hartree Fock

This article presents N2+ fragment yields following nitrogen K-shell photo-absorption in the NH+ molecular ion measured at the SOLEIL synchrotron radiation facility in the photon energy region 390–450 eV. The combination of the high sensitivity of the merged-beam, multi-analysis ion apparatus (MAIA) with the high spectral resolution of the PLEIADES beamline helped to resolve experimentally vibrational structures of highly excited [N1s−1H]*+ electronic states with closed or open-shell configurations. The assignment of the observed spectral features was achieved with the help of density functional theory (DFT) and post-Hartree Fock Multiconfiguration Self-Consistent-Field/Configuration Interaction (MCSCF/CI) ab-initio theoretical calculations of the N1s core-to-valence and core-to-Rydberg excitations, including vibrational dynamics. New resonances were identified compared to previous work, owing to detailed molecular modeling of the vibrational, spin-orbit coupling and metastable state effects on the spectra. The latter are evidenced by spectral contributions from the 4Σ− electronic state which lies 0.07 eV above the NH+2Π ground state.

scholarly journals Investigation of the cis–trans structures and isomerization of oligoprolines by using Raman spectroscopy and density functional theory calculations: solute–solvent interactions and effects of terminal positively charged amino acid residues

RSC Advances ◽  
2020 ◽  
Vol 10 (57) ◽  
pp. 34493-34500
Author(s):  
Mei-Chun Huang ◽  
Wei-Hao Chen ◽  
Chen-Wei Huang ◽  
Kuei-Yen Huang ◽  
Jia-Cherng Horng ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Raman Spectroscopy ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Density Functional Theory Calculations ◽  
State Density ◽  
Amino Acid Residues ◽  
Functional Theory ◽  
Solvent Interactions ◽  
Positively Charged

The low-wavenumber Raman spectra in combination with theoretical calculations via solid-state density functional theory (DFT)-D3 are displayed. The vibrational structures and interaction with solvent of poly-l-proline and the oligoproline P12 series are identified.

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