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Atomic charges in Mg2SiO4 (forsterite), fitted to thermoelastic and structural properties

1982; Elsevier BV; Volume: 43; Issue: 12 Linguagem: Inglês

10.1016/0022-3697(82)90139-1

1879-2553

M. Catti,

Advanced ceramic materials synthesis

First and second derivatives of cohesion energy of forsterite with respect to cell edges (generalized Born-Mayer model) are related to thermoelastic tensors; first derivatives with respect to five structural parameters (rotation angle of the SiO4 tetrahedron, translations of Si and Mg(2) atoms) are set equal to zero by the zero-force principle. All differentiations are performed by keeping constant the internal geometry of the SiO4 group. Fourteen equations are then obtained and solved numerically in the magnesium and oxygen atomic charges, and in three repulsive parameters, considered as unknowns. The best fitting charge distribution is: zMg = 1.38, zo = −1.05, zsi = l.44 e. Elastic constants are reproduced with an average relative deviation of 4%, and calculated atomic positions show an average shift of 0.014 A from experimental values. Results are discussed and compared with atomic charges determined from X-ray electron density measurements and vibrational spectroseopy data.