scholarly journals Unknown Knowns: Case Studies in Uncertainties in the Computation of Thermochemical Parameters

2020 ◽  
Author(s):  
John Simmie
Keyword(s):  
Heat Capacity ◽  
Gas Phase ◽  
Basis Set ◽  
Statistical Thermodynamic ◽  
Vibrational Modes ◽  
Heavy Atoms ◽  
New Methods ◽  
Formation Enthalpies ◽  
Thermochemical Parameters

<div>Both the computation of, and the uncertainties associated, with gas-phase molar formation enthalpies are now quite well established for systems comprised of tens of ‘heavy’ atoms chosen from the commonest elements. The same cannot be said for derived thermochemical quantities such as entropy, heat capacity and an enthalpy function. Whilst the application of well known statistical thermodynamic relations is mostly understood, the determination of the uncertainty with which such values can be obtained has been little studied — apart, that is, for a general protocol devised by Goldsmith et al. [J. Phys. Chem. A, 2012, 116, 9033–9057]. Specific examples from that work are explored here and it is shown that their estimates are overly pessimistic. It is also evident that for some species the calculated thermochemical parameters show very little variation with either the level of theory, or basis set, or treatment of vibrational modes — this renders the inclusion of such species in databases designed to validate new methods of limited value.<br></div>

scholarly journals Unknown Knowns: Case Studies in Uncertainties in the Computation of Thermochemical Parameters

2020 ◽  
Author(s):  
John Simmie
Keyword(s):  
Heat Capacity ◽  
Gas Phase ◽  
Basis Set ◽  
Statistical Thermodynamic ◽  
Vibrational Modes ◽  
Heavy Atoms ◽  
New Methods ◽  
Formation Enthalpies ◽  
Thermochemical Parameters

<div>Both the computation of, and the uncertainties associated, with gas-phase molar formation enthalpies are now quite well established for systems comprised of tens of ‘heavy’ atoms chosen from the commonest elements. The same cannot be said for derived thermochemical quantities such as entropy, heat capacity and an enthalpy function. Whilst the application of well known statistical thermodynamic relations is mostly understood, the determination of the uncertainty with which such values can be obtained has been little studied — apart, that is, for a general protocol devised by Goldsmith et al. [J. Phys. Chem. A, 2012, 116, 9033–9057]. Specific examples from that work are explored here and it is shown that their estimates are overly pessimistic. It is also evident that for some species the calculated thermochemical parameters show very little variation with either the level of theory, or basis set, or treatment of vibrational modes — this renders the inclusion of such species in databases designed to validate new methods of limited value.<br></div>

Low-energy vibrational spectra of flexible diphenyl molecules: biphenyl, diphenylmethane, bibenzyl and 2-, 3- and 4-phenyltoluene

2014 ◽  
Vol 16 (40) ◽  
pp. 22062-22072 ◽  
Author(s):  
M. A. Martin-Drumel ◽  
O. Pirali ◽  
C. Falvo ◽  
P. Parneix ◽  
A. Gamboa ◽  
...  
Keyword(s):  
Gas Phase ◽  
Vibrational Spectra ◽  
Accurate Determination ◽  
Low Frequency ◽  
Low Energy ◽  
Vibrational Modes ◽  
Phase Spectra

Gas phase spectra of six bi-phenyl molecules are reported allowing an accurate determination of their active low-frequency vibrational modes.

scholarly journals THERMOCHEMICAL PARAMETERS OF ERGOTHIONEINE: A DFT STUDY USING M06, WB97XD AND TPSSTPSS METHODS

2018 ◽  
Vol 54 (2C) ◽  
pp. 299
Author(s):  
Chinh Thi Ngo
Keyword(s):  
Gas Phase ◽  
Antioxidant Properties ◽  
Basis Set ◽  
Bond Dissociation Enthalpy ◽  
Single Electron Transfer ◽  
Dft Methods ◽  
Dissociation Enthalpy ◽  
Proton Dissociation ◽  
B3lyp Method ◽  
Thermochemical Parameters

Antioxidant properties of ergothioneine (ESH) have been investigated via hydrogen atomtransfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential proton losselectron transfer (SPLET) mechanisms. Three new DFT methods including M06, WB97XD andTPSSTPSS at the 6-311++G(2df,2p) basis set were used to compute the thermochemicalparameters of ESH in the gas phase. Based on these methods, bond dissociation enthalpy (BDE),ionization energy (IE), proton dissociation enthalpy (PDE), proton affinity (PA) and electrontransfer enthalpy (ETE) were calculated. The results were also compared with the valuesobtained by B3LYP method. The calculated results show that ergothioneine plays a role as apotential antioxidant via HAT mechanism.

Intrinsic Stacking Interactions of Natural and Artificial Nucleobases

2019 ◽  
Author(s):  
Drew P. Harding ◽  
Laura J. Kingsley ◽  
Glen Spraggon ◽  
Steven Wheeler
Keyword(s):  
Gas Phase ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Molecular Descriptors ◽  
Stacking Interactions ◽  
Interaction Energies ◽  
Functional Theory ◽  
Binding Partner ◽  
Heavy Atoms ◽  
Wide Range

The intrinsic (gas-phase) stacking energies of natural and artificial nucleobases were explored using density functional theory (DFT) and correlated ab initio methods. Ranking the stacking strength of natural nucleobase dimers revealed a preference in binding partner similar to that seen from experiments, namely G > C > A > T > U. Decomposition of these interaction energies using symmetry-adapted perturbation theory (SAPT) showed that these dispersion dominated interactions are modulated by electrostatics. Artificial nucleobases showed a similar stacking preference for natural nucleobases and were also modulated by electrostatic interactions. A robust predictive multivariate model was developed that quantitively predicts the maximum stacking interaction between natural and a wide range of artificial nucleobases using molecular descriptors based on computed electrostatic potentials (ESPs) and the number of heavy atoms. This model should find utility in designing artificial nucleobase analogs that exhibit stacking interactions comparable to those of natural nucleobases. Further analysis of the descriptors in this model unveil the origin of superior stacking abilities of certain nucleobases, including cytosine and guanine.

On the trustability of semi-empirical methods to the calculation of gas phase formation enthalpies of inorganic compounds containing heavy metals: tin borates

2017 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Heavy Metals ◽  
Gas Phase ◽  
Phase Formation ◽  
Inorganic Compounds ◽  
Formation Enthalpy ◽  
Computational Time ◽  
Gas Formation ◽  
Formation Enthalpies ◽  
Knudsen Effusion Mass Spectrometry ◽  
Semi Empirical

<p>In the present work, are calculated the gas formation enthalpies (SE; PM3 and PM6) for tin borates: SnB<sub>2</sub>O<sub>4</sub><sup> </sup>and Sn<sub>2</sub>B<sub>2</sub>O<sub>5</sub>. The calculated values are compared with experimental ones, obtained by Knudsen effusion mass spectrometry [3]. It is shown that SE methods, besides their lower computational time consuming can, indeed, provide reliable gas phase formation enthalpy values for inorganic compounds containing heavy metals.</p>

Changes of some sewage sludge parameters prepared with an ultrasonic field

1997 ◽  
Vol 36 (11) ◽  
pp. 101-106 ◽  
Author(s):  
January Bien ◽  
Lidia Wolny
Keyword(s):  
Sewage Sludge ◽  
Microscopic Analysis ◽  
Chemical Compounds ◽  
Ultrasonic Field ◽  
Water Removal ◽  
Vacuum Filter ◽  
Additional Criterion ◽  
New Methods ◽  
Sludge Conditioning

Studies of sewage sludge conditioning by ultrasonic field concentrate on determination of the increase of water removal effect, which depends on kind of sludge and chemical compounds used in the dewatering process. An attempt was made to find new methods of sludge preparation before dewatering. Tests presented here focused on digested and difficult dewatered sludge. The sludge was dewatered on a vacuum filter after conditioning with polyelectrolytes and the ultrasonic field. The microscopic analysis was an additional criterion to evaluate changes in the sludge structure after preparation. The polyelectrolyte dose of 3 mg/g d.m. sonicated within 15 sec. resulted in the 50% decrease of sludge volume. Results presented confirmed our previous experiences, concerning the relation between conglomerates of sludge and the effect of dewatering.

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