Ab Initio Studies Of Hydrogen Research Articles

Ab initio study of hydrogen sensing in Pd and Pt functionalized GaN [0 0 0 1] nanowires

Using density functional theory based simulations, the adsorption of hydrogen on GaN nanowires with [0 0 0 1] orientation is studied with Pt and Pd functionalization. The adsorption energies show that both Pt and Pd prefer to attach to a top site above the Ga atom in the nanowire. In the pristine GaN, hydrogen attach as a molecule, while in the presence of Pt and Pd, it dissociates into atoms and adsorb through a chemical bonding. Change in Ga-N bond lengths are observed with hydrogen adsorption on the surface of the nanowire and the resultant strain as well as the charge transfer between atoms can be used as entities to understand the detection mechanism. From the electronic structure analysis, it is revealed that both Pt and Pd can be used to tune the band gap and are favorable adsorbates to enhance the hydrogen sensing properties of GaN nanowires. Pt turns out to be a more efficient adsorbate for hydrogen detection due to the lowered adsorption energies, compact Pt-H bond length and enhanced surface charge reconstruction.

Ab initio study of hydrogen bonding in the H3PO2 dimer and H3PO2-DMF complex.

The molecular structures and H-bonding interactions in the phosphinic acid dimer and the complex of phosphinic acid with N,N-dimethylformamide (DMF) were investigated by density functional theory calculations at the B3LYP level of theory. In order to better understand these phenomena, the individual molecules were also studied. The results were compared with previously obtained data for similar H-bonded complexes of phosphoric and phosphorous acids with DMF. Various correlations were found between geometric characteristics and parameters derived from Bader's theory and natural bond orbital analysis. Graphical abstract Irina V. Fedorova and Lyubov P. Safonova. Ab initio study of hydrogen bonding in the H3PO2 dimer and H3PO2-DMF complex. The acids of phosphorus are considered suitable candidates for ionomers due to their efficient proton transport properties. In order to better understand their molecular structures and their H-bond characteristics in real liquids, the most stable configurations of the H3PO2 dimer and the H3PO2-DMF complex were examined using computational methods in quantum chemistry. It was found that the strength of the H-bonding interactions in these systems depends strongly on the environment.

Ab initio studies of hydrogen and acceptor defects in rutile TiO2

The behaviour of hydrogen in both defect free and acceptor doped bulk rutile TiO2 is investigated through defect calculations performed within the density functional theory formalism. Both interstitial and substitutional hydrogen defects are shown to behave as shallow donors in the material, thereby existing as effectively positive hydroxide defects, OH*(O), and substitutional hydrogen defects, H*O. Of the investigated isolated hydrogen defects, the OH*(O) defect is shown to have the lowest formation energy over the whole Fermi level range under both oxidising and reducing conditions. However, the formation energy of H*O is only 0.35 eV higher under conditions where TiO2 is in equilibrium with Ti2O3, indicating that it exists as a minority defect in rutile TiO2 under highly reducing conditions such as under growth of TiO2 on a Ti metal surface. The enthalpy of hydration of oxygen vacancies is calculated to be -1.64 and -1.60 eV for the 2 x 2 x 3 and 3 x 3 x 3 supercells, indicating that OH*(O) defects will prevail in wet atmospheres, even at high temperatures. Hydrogen incorporated in the material can furthermore be expected to associate significantly with various acceptor centres (e.g., substitutional N and Al acceptors and Ti vacancies). The binding energies of the substitutional NH(x)O (imide) defect and of the association complexes between H and fully ionised substitutional Al, (Al'Ti x OH*(O)), and Ti vacancies, (V(Ti)x OH*(O)and (V(Ti) x 4OH*(O)) (i.e., Ruetschi type defects), are calculated to be -0.36, -0.12, -0.47 and -0.82 eV, respectively.

Ab initio study of hydrogen bonding interaction and photoinduced electron transfer between 4‐nitroquinoline‐1‐oxide and tryptophan

AbstractIn the present article, the electronic structure of 4‐nitroquinoline‐1‐oxide (4NQO) has been theoretically investigated at the level of HFSCF/6‐31G**. Conformation of monomeric 4NQO has been found to be the most stable when the nitro group twists from the quinoline plane by about 24°. The absorption spectra of the twisted 4NQO have been calculated by using complete active space self‐consistent field method. The hydrogen bonded complexes of 4NQO and tryptophan have been intensively studied. The absorption spectra of the most stable complex have been calculated to investigate the photoinduced electron transfer between 4NQO and tryptophan. The first and second excited singlet states are found to be charge‐separated. Population analysis shows that the low‐lying triplet states are charge‐separated as well, except for the lowest one that presents the characters of a locally excited state. A solvent effect on transition energies has been considered based on the Ooshika–Lippert–Martaga equation. Theoretical study shows that the optical excitation can lead to charge separation in the 4NQO–tryptophan complex. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Infrared and ab initio studies of hydrogen bonding and proton transfer in the complexes formed by pyrazoles

The results of experimental studies and quantum mechanical calculations of vibrational spectra and structure of hydrogen bonded complexes formed by pyrazole (P) and 3,5-dimethylpyrazole (DMP) are presented. IR spectra of pyrazoles in solutions, gas phase, and solid state have been investigated in wide range of concentrations and temperatures. It has been found that in the gas phase both P and DMP reveal the equilibrium between monomers, dimers, and trimers. In solutions the equilibrium between monomers and trimers dominates, no bands, which can be attributed to dimers were detected. DMP retains the trimer structure in solid state, while in the case of pyrazole P, formation of the crystal provides another type of association. Geometrical and spectral characteristics of dimers and trimers, obtained by ab initio calculations, are presented and compared with experimental data. IR spectra of solutions containing P and DMP with a number of acids (acetic and trifluoroacetic acids, pentachlorophenol, HBr) have been studied in parallel with ab initio calculations. It has been found that pentachlorophenol forms with pyrazoles complexes with one strong hydrogen bond O–H⋯N, while NH pyrazole group remains unbonded. With carboxylic acids DMP forms 1:1 cyclic complexes with two hydrogen bonds. In the case of acetic acid, the complex in CH 2Cl 2 solution reveals molecular structure with OH⋯N and CO⋯HN bonds, in accordance with results of the calculations. For trifluoroacetic acid, the calculations predict the molecular structure to be energetically more stable in the case of the isolated binary complex (in gas phase), while the experimental spectrum of CH 2Cl 2 solution gives an evidence of the proton transfer with formation of the cyclic ionic pair with two NH +⋯O − bonds. The agreement with experimental results can be improved by taking into account the influence of environment in the framework of Onsager or Tomasi models. The shape of proton potential function of the complexes and medium effect on its parameters, resulted from experimental data and calculations, are discussed. It has been found that the number of potential minima and their relative depth depend strongly on the method of calculations and the basic set. Under excess of trifluoroacetic acid, the formation of 2:1 acid–DMP complex has been detected. Spectral characteristics and results of calculations point to the cyclic structure of this complex, which includes homoconjugated bis-trifluoroacetate anion and DMPH + cation. With HBr both studied pyrazoles were found to form ionic complexes including one or two pyrazole molecules per one acid molecule and correspondingly monocation or homoconjugated cation BHB +.

An ab initio study of hydrogen in forsterite and a possible mechanism for hydrolytic weakening

Even small amounts of water can profoundly effect the physical properties of minerals. In olivine <1 H in every 1000 unit cells acts to increase creep rates of dunite by ∼ 2 orders of magnitude. Although the mechanism for this is not known, it is not unreasonable to suggest that it is in some way related to an increase in the point defect population. In order to understand this better we have performed ab initio pseudopotential calculations within the generalized gradient approximation on protonic defects in Mg2SiO4 forsterite. Three mechanisms for incorporating protons are considered: (1) interstitial, (2) binding at cation vacancies, and (3) binding at silicon vacancies. Assuming the existence of both Si and Mg vacancies, on energetic considerations, protons will initially populate Si vacancies until there are three protons in the vacancy. At this point, the addition of one more proton (to make a hydrogarnet substitution) is energetically unfavourable in comparison to populating the Mg vacancy, and the next proton will enter the Mg site. Interstitial protons will be very rare. Since it is >2 eV more favourable to put the first proton into the Si vacancy than the magnesium site, the presence of water will certainly act to increase the population of silicon vacancies. In fact, in the presence of water the energy required to form a Si vacancy is perhaps less than that to form an Mg vacancy. This is in stark contrast to dry olivine where Si vacancies are many eV less favourable. If creep is rate limited by the diffusion of the slowest species, silicon in olivine, then increasing the Si vacancy concentration could provide a mechanism for hydrolytic weakening.

Ab initio studies of hydrogen bonding of N-methylacetamide: structure, cooperativity, and internal rotational barriers

Hydrogen bonding interactions and their effect on the structure and the energetics of the rotation about N-C α and C α -C' bonds are studied for N-methylacetamide (NMA) by use of ab initio quantum mechanical calculations. The structure and methyl rotational barriers for isolated NMA have been determined at the Hartree-Fock (HF) level with 6-31G, 6-31G * , and 6-31G ** basis sets and at the second-order MOller-Plesset perturbation (MP2) level with a 6-31G * basis set including geometry optimization for the different methyl orientations

ChemInform Abstract: Ab Initio Study of Hydrogen, Lithium and Sodium Bonding on the Basis of Atomic Charges, Valencies, Bond Orders and Overlap Populations

ChemInformVolume 19, Issue 21 Physical Inorganic Chemistry ChemInform Abstract: Ab Initio Study of Hydrogen, Lithium and Sodium Bonding on the Basis of Atomic Charges, Valencies, Bond Orders and Overlap Populations T. KAR, T. KAR Dep. Chem., Indian Inst. Technol., Kharagpur 721 302Search for more papers by this authorA. B. SANNIGRAHI, A. B. SANNIGRAHI Dep. Chem., Indian Inst. Technol., Kharagpur 721 302Search for more papers by this authorB. G. NIYOGI, B. G. NIYOGI Dep. Chem., Indian Inst. Technol., Kharagpur 721 302Search for more papers by this author T. KAR, T. KAR Dep. Chem., Indian Inst. Technol., Kharagpur 721 302Search for more papers by this authorA. B. SANNIGRAHI, A. B. SANNIGRAHI Dep. Chem., Indian Inst. Technol., Kharagpur 721 302Search for more papers by this authorB. G. NIYOGI, B. G. NIYOGI Dep. Chem., Indian Inst. Technol., Kharagpur 721 302Search for more papers by this author First published: May 24, 1988 https://doi.org/10.1002/chin.198821004Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume19, Issue21May 24, 1988 RelatedInformation

Ab initio studies of hydrogen bonding in the complexes of HNC, HCP, FCN, ClCN and BrCN with HF, HCl and HBr

Large basis set gaussian orbital SCF-MO calculations are presented for the hydrogen-bonded complexes formed between HNC, HCP, FCN, ClCN and BrCN with HF, HCl and HBr. Calculated equilibrium geometries, hydrogen bond energies and various one-electron properties are given to supplement available experimental data. Changes in electron distribution on complex formation are discussed in terms of Mulliken population analysis indices.

Comment on the strongest type of hydrogen bond

Ab initio studies of hydrogen bonding in the carboxylic acid-fluoride systems apply to the free state. In condensed phases strong interactions lead to more complex structures. IR spectra of saturated solutions and solid solvates indicate at least two different types of hydrogen bond. The high solvation energy of the fluoride anion enables different ionic and molecular species to coexist.

Ab initio studies of hydrogen bonding between peptide units. IV. The mutual orientations of the peptide planes

It is shown by SCF MO LCGO computations that no energy loss occurs in linearly hydrogen-bonded peptides when the plane of one peptide unit is rotated around the hydrogen bond from 0 to 90 degress. Both the nuclear-nuclear and electron-electron repulsions decrease upon rotation, but their decrease is compensated by an increase in the one-electron attractive terms. The first and second order components of the energy remain constant as well as the amount of electrons transferred.