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Titolo:
Density functional theory calculations of hydrogen-containing defects in forsterite, periclase, and alpha-quartz
Autore:
de Leeuw, NH;
Indirizzi:
Univ Reading, Dept Chem, Reading RG6 6AD, Berks, England Univ Reading Reading Berks England RG6 6AD eading RG6 6AD, Berks, England
Titolo Testata:
JOURNAL OF PHYSICAL CHEMISTRY B
fascicolo: 40, volume: 105, anno: 2001,
pagine: 9747 - 9754
SICI:
1520-6106(20011011)105:40<9747:DFTCOH>2.0.ZU;2-2
Fonte:
ISI
Lingua:
ENG
Soggetto:
INITIO MOLECULAR-DYNAMICS; TOTAL-ENERGY CALCULATIONS; WAVE BASIS-SET; CRYSTAL-GROWTH; SURFACE-STRUCTURE; ELECTRONIC-STRUCTURE; COMPUTER-SIMULATION; MAGNESIUM-OXIDE; MGO; ADSORPTION;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
72
Recensione:
Indirizzi per estratti:
Indirizzo: de Leeuw, NH Univ Reading, Dept Chem, POB 224, Reading RG6 6AD, Berks, England Univ Reading POB 224 Reading Berks England RG6 6AD s, England
Citazione:
N.H. de Leeuw, "Density functional theory calculations of hydrogen-containing defects in forsterite, periclase, and alpha-quartz", J PHYS CH B, 105(40), 2001, pp. 9747-9754

Abstract

Electronic structure calculations using the density functional theory within the generalized-gradient approximation and ultra-soft pseudopotentials have been used to investigate the absorption of water and protons in forsterite Mg2SiO4, periclase (MgO), and alpha -quartz (alpha -SiO2). The calculated, structural parameters are found to be in good agreement with experiment. Absorption of water in the perfect lattice is calculated to be an endothermic process in all three minerals but exothermic when associatively adsorbed at the forsterite {010} surface. The introduction of cation vacancies inthe lattices is energetically unfavorable, more so for the formation of a silicon vacancy than a magnesium vacancy. The process of introducing a neutral silicon vacancy in the lattice, by reaction of a silicon atom with gaseous oxygen to form SiO2, is endothermic by approximately the same amount ofenergy (approximately 430 kJ mol(-1)) in both quartz and forsterite, but introducing an equivalent magnesium vacancy in the periclase lattice is lessendothermic (163 kJ mol(-1)) than the same process in forsterite (217 kJ mol(-1)). Absorption of hydrogen molecules at the vacant cation sites is a highly exothermic process, releasing on average between 213 and 273 kJ mol(-1) per proton when absorbed at a magnesium vacancy and approximately 275 kJmol(-1) per proton at a vacant silicon site. When we calculate the replacement of MgO and SiO2 units by liquid water molecules, as a first step in the process of dissolution of the minerals, we find that it is an endothermicprocess in the bulk minerals but exothermic by 71 kJ mol(-1) for replacingan MgO unit at the forsterite {010} surface.

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Documento generato il 29/09/20 alle ore 08:18:47