ISSN:
0192-8651
Schlagwort(e):
Computational Chemistry and Molecular Modeling
;
Biochemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Informatik
Notizen:
Ab-initio self-consistent-field molecular-orbital (SCF MO) Hartree-Fock (HF) calculations using the STO-3G, 6-31G, and 6-31G* basis sets, were performed to model quasi-tetrahedral silicon species in silicon dioxide. Mostly nine-atom clusters, [Si(OH)4]qt, with charge number qt = 0 or + 1, were studied. The positions of the Si and O atoms were varied to achieve minimum total energies, while the protons were held fixed in the O-(neighboring)Si direction to simulate the rigid crystal surroundings. The α-quartz-type local symmetry C2 was found to be retained for the neutral cluster, but not for the ionic one. The unrestricted HF calculations indicate that the latter paramagnetic centre, (qt = +1), has its spin population almost entirely on one short-bonded oxygen ion bonded weakly to its neighboring Si, and is quite high in energy (9.55 eV with 6-31G) compared to the diamagnetic centre (qt = 0). The ionization energy is much higher than the self-trapping potential of the polaronic hole, a fact which may account for the failure so far to observe a [SiO4]+1 center in quartz by means of continuous-wave electron paramagnetic resonance spectroscopy. Calculations on the [SiO4]+1 center agree well with ultraviolet spectra, and with the [hole portion of a] proposed radiation-induced exciton in quartz. The hole in [Si(OH)4]+1 can be shifted from a short-bonded to a long-bonded oxygen to give the excited state [Si(OH)4]es+1. Conclusions reached with the nine-atom clusters were confirmed by a series of calculations on the extended model [Si(OSiH3)4]qt. Comparisons with the known isoelectronic species [AlO4]0 were carried out.
Zusätzliches Material:
4 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/jcc.540120216
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