PERIODIC HARTREE–FOCK CALCULATION OF THE OXIDATION OF Si(111)

1999 ◽  
Vol 06 (06) ◽  
pp. 1031-1036 ◽  
Author(s):  
PHILIPPE SONNET ◽  
LOUISE STAUFFER ◽  
CHRISTIAN MINOT
Keyword(s):  
Oxygen Atom ◽  
Local Minimum ◽  
Atomic Oxygen ◽  
Potential Surface ◽  
Early Stage ◽  
Heat Of Adsorption ◽  
Molecular Adsorption ◽  
Hartree Fock

We present Hartree–Fock calculations of the adsorption of oxygen on a Si(111)-(2×2) surface, which models the Si(111)-(7×7) structure, including its two main sites (adatom and rest atom sites). In the most stable configurations, molecules dissociate leading to atomic oxygen bridging the adatom backbonds. The molecular adsorption is less favorable. The dioxygen, however, is a local minimum of the potential surface in two cases: (i) in the "grif" geometry; (ii) bridging between a rest atom and an adatom. It then represents a possible precursor for the early stage of oxidation. The presence of an oxygen atom already adsorbed on the surface enhances the heat of adsorption of other oxygen (atomic or molecular) on the same site.

scholarly journals The O(<sup>1</sup>S) dayglow emission as observed by the WIND imaging interferometer on the UARS

1996 ◽  
Vol 14 (6) ◽  
pp. 637-646 ◽  
Author(s):  
V. Singh ◽  
I. C. McDade ◽  
G. G. Shepherd ◽  
B. H. Solheim ◽  
W. E. Ward
Keyword(s):  
Oxygen Atom ◽  
Atomic Oxygen ◽  
Lower Thermosphere ◽  
Dissociative Recombination ◽  
Model Atmosphere ◽  
Emission Rates ◽  
Imaging Interferometer ◽  
Volume Emission ◽  
Excitation Mechanisms ◽  
Three Body

Abstract. Volume emission rate profiles of the O(1D-1S) 5577 Å dayglow measured by the WIND imaging interferometer on the Upper Atmosphere Research Satellite are analyzed to examine the O(1S) excitation mechanisms in the sunlit lower thermosphere and upper mesosphere. The observed emission profiles are compared with theoretical profiles calculated using a model which takes into account all of the known daytime sources of O(1S). These include photoelectron impact on atomic oxygen, dissociative recombination of O+2, photodissociation of molecular oxygen, energy transfer from metastable N2(A3Σ+u) and three body recombination of atomic oxygen. Throughout most of the thermosphere the measured and modelled emission rates are in reasonably good agreement, given the limitations of the model, but in the region below 100 km, where the oxygen atom recombination source is likely to dominate, the measured emission rates are considerably larger than those modelled using the MSIS-90 oxygen atom densities. This discrepancy is discussed in terms of possible inadequacies in the MSIS-90 model atmosphere and/or additional sources of O(1S) at low altitude.

First-Principle Calculation of Monovacancy and Divacancy Interactions with Atomic Oxygen in Nickel: Thermal Expansion Effects

2009 ◽  
Vol 289-292 ◽  
pp. 747-753 ◽  
Author(s):  
Claude Mijoule ◽  
El Hocine Megchiche ◽  
Eric Andrieu ◽  
Daniel Monceau
Keyword(s):  
Thermal Expansion ◽  
Oxygen Atom ◽  
Atomic Oxygen ◽  
First Principle ◽  
Migration Process ◽  
Principle Calculation ◽  
First Principle Calculation ◽  
Substitution Site ◽  
Defect System ◽  
And Diffusion

The insertion and diffusion energies of oxygen in presence of vacancies in nickel are studied by using the first-principle projector augmented waves (PAW). When the oxygen atom is located in a substitution site, the formation of a vacancy-oxygen pair is observed. Furthermore, we show that the formation of divacancies allows the oxygen atom to migrate more easily in the metal. A model for the migration process of the three-defect system is proposed. Finally, thermal expansion effects are included in our study; it is shown that temperature effects emphasize the diffusion.

Ab initio studies of isocyanatoborane and difluoroisocyanatoborane; bent or linear BNCO chains?

1991 ◽  
Vol 69 (6) ◽  
pp. 1000-1005 ◽  
Author(s):  
Susan Ellis ◽  
Edward G. Livingstone ◽  
Nicholas P. C. Westwood
Keyword(s):  
Carbon Atom ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Potential Surface ◽  
Energy Difference ◽  
Basis Set ◽  
Basis Sets ◽  
Hartree Fock ◽  
Split Valence ◽  
Valence Basis Set

Ab initio calculating at the 3-21G, 6-31G*, 6-31G**, 6-311G*, and 6-311G** Hartree–Fock levels, have been performed on the unknown H2BNCO and F2BNCO molecules in order to establish the geometries of these isoelectronic propadienone analogues. For H2BNCO the double split valence basis sets lead to linear BNCO chains, whereas either a triple split valence basis set, or the inclusion of correlation to second order (MP2/6-31G*) gives trans-bent structures. These have angles at nitrogen of 153.6° (6-311G*) or 149.9° (MP2/6-31G*), with the potential surface for angle bending extremely flat, and 0.5 kJ mol−1 (6-311 G*) or 1.12 kJ mol−1 (MP2/6-31 G*) separating the C2v and Cs structures. For the bent structures there is a small trans-bend (4–6°) at the carbon atom. The F2BNCO molecule is also linear at the 3-21G level, but is, however, already trans-bent (145.6° at nitrogen, 175.9° at carbon) at the 6-31G* Hartree–Fock level; 1.47 kJ mol−1 separates the bent and linear structures. The triple split valence basis set 6-311G* leads to a further decrease in the angle at nitrogen (141.0°), and a similar NCO angle (175.9°), with the bent structure favoured by 3.85 kJ mol−1. MP2/6-31G* calculations give a minimum with an angle at nitrogen of 140.2°, and a bent-linear energy difference of 3.58 kJ mol−1. Key words: ab initio calculations, isocyanatoboranes, structures, quasilinearity, propadienone analogues.

Nitrosyl cyanide and related aspects of the ONCN potential surface

1978 ◽  
Vol 31 (11) ◽  
pp. 2349 ◽  
Author(s):  
BG Gowenlock ◽  
L Radom
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Related Species ◽  
Potential Surface ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Hartree Fock ◽  
Split Valence ◽  
Good Agreement

Ab initio molecular orbital calculations using the restricted Hartree-Fock approach have been carried out for nitrosyl cyanide and related species on the ONCN potential surface. Full geometry optimizations have been performed with the minimal STO-3G and split-valence 4-31G basis sets. Calculated (4-31G) geometries are in good agreement with available experimental data as are the energy changes in the reactions ONCN → NO + CN and NO + CN → N2 + CO. Possible mechanisms are discussed.

CHEMISORPTIONS OF ATOMIC OXYGEN AND ITS REPLACEMENT BY HYDROGEN ON THE DIAMOND (100) SURFACE STUDIED BY FIRST PRINCIPLES

2006 ◽  
Vol 13 (01) ◽  
pp. 45-49 ◽  
Author(s):  
Z. G. WANG ◽  
X. T. ZU ◽  
J. L. NIE ◽  
H. Y. XIAO
Keyword(s):  
Oxygen Atom ◽  
First Principles ◽  
Atomic Oxygen ◽  
Oxidation Process ◽  
Bridge Structure ◽  
First Principles Calculations ◽  
Initial Oxidation ◽  
Oxidized Diamond

The initial oxidation process of a clean diamond (100) surface was studied by first-principles calculations. The O -bridge with C–O–C bond chemisorption, O -on-dimer chemisorption with epoxy structure, and O -on-top chemisorption with C=O bond structure are found to be stable on the diamond (100) surfaces. The epoxy structure is more stable than the O -bridge structure. The calculation also shows that the oxygen atom can be replaced by hydrogen in the oxidized diamond (100) surface.

scholarly journals A Theoretical Study of the Conformational Changes in Hydrazine

1974 ◽  
Vol 52 (15) ◽  
pp. 2785-2791 ◽  
Author(s):  
John O. Jarvie ◽  
Arvi Rauk
Keyword(s):  
Dihedral Angle ◽  
Conformational Changes ◽  
Theoretical Study ◽  
Potential Surface ◽  
Experimental Results ◽  
Hartree Fock ◽  
Pyramidal Inversion ◽  
Bond Functions ◽  
Torsional Component ◽  
Substituted Hydrazines

Abinitio restricted Hartree–Fock–Roothaan l.c.a.o.–m.o.–s.c.f. calculations using a Gaussian lobe basis with bond functions have been performed to determine the characteristics of the potential surface for nuclear motions in hydrazine. It was found that in its equilibrium conformation the molecule has a dihedral angle of 95°. The barrier to pyramidal inversion at one nitrogen is 6.1 kcal/mol and the syn and anti rotational barriers are calculated to be 12.0 and 1.6 kcal/mol, respectively. There is a very slight torsional component in the inversion pathway. During rotation over the anti barrier the bond angles contract from their average equilibrium value of 109.5° to 105.3°. This contraction appears to be an important feature of the rotational potential curve. Features of the surface are used to rationalize experimental results in cyclic and acyclic substituted hydrazines.

FULLERENE DERIVATIVES: STRUCTURES AND STABILITIES OF C60O AND C70O

1992 ◽  
Vol 06 (23n24) ◽  
pp. 3821-3831 ◽  
Author(s):  
KRISHNAN RAGHAVACHARI
Keyword(s):  
Oxygen Atom ◽  
Infrared Spectra ◽  
Ground State ◽  
Membered Ring ◽  
Low Energy ◽  
Fullerene Derivatives ◽  
Hartree Fock ◽  
Semi Empirical ◽  
Very High ◽  
C Nmr

Semi-empirical (MNDO) and ab-initio Hartree-Fock (3–21G) calculations on the structures and stabilities of C 60 O and C 70 O are reported. Two low energy isomers of C 60 O , formed by an oxygen atom bridging the two different C–C bonds in C 60, have been found. The first isomer has an epoxide structure with a bridging oxygen across the bond between two fused six-membered rings in C 60 (bridging C–C≈1.6 Å). Its 13 C NMR and infrared spectra are consistent with those seen for the experimentally isolated form of C 60 O . However, the second isomer containing a bridging oxygen across the bond between a five- and a six-membered ring is slightly more stable and appears to be the ground state of C 60 O . The bridging C–C bond opens out to a distance of ≈2.1 Å in this isomer. Endohedral isomers of C 60 O are calculated to be very high in energy. For C 70 O , we have characterized eight isomers formed by an oxygen atom bridging each of the eight distinct C–C bonds in C 70. The ground state isomer corresponds to oxygen bridging across an equatorial C–C bond in C 70 which opens out to a distance of ≈2.2 Å. This structure is different from the bridged paracyclene-like isomer proposed previously for C 70 O . Comparison is made between C 60 O and C 70 O .

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