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On a proposed radiation‐induced polaronic hole in silicon dioxide
Author(s) -
Rao P. S.,
McEachern R. J.,
Weil J. A.
Publication year - 1991
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540120216
Subject(s) - excited state , chemistry , paramagnetism , atomic physics , ionic bonding , ab initio , ab initio quantum chemistry methods , atom (system on chip) , binding energy , ionization energy , ionization , ion , molecular physics , condensed matter physics , physics , molecule , organic chemistry , computer science , embedded system
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 q t = 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 C 2 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, ( q t = +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 ( q t = 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 [SiO 4 ] +1 center in quartz by means of continuous‐wave electron paramagnetic resonance spectroscopy. Calculations on the [SiO 4 ] +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(OSiH 3 ) 4 ] qt . Comparisons with the known isoelectronic species [AlO 4 ] 0 were carried out.