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The anisotropy of dielectric properties in the orthorhombic and hexagonal structures of Anhydrite – an ab initio and hybrid DFT study
Author(s) -
Mallia Giuseppe,
Dovesi Roberto,
Corà Furio
Publication year - 2006
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.200642161
Subject(s) - orthorhombic crystal system , anisotropy , ab initio , chemistry , dielectric , ab initio quantum chemistry methods , condensed matter physics , ionic bonding , ion , crystallography , computational chemistry , physics , molecule , crystal structure , quantum mechanics , organic chemistry
The effects of an electric field on the electronic properties of a typical ionic‐covalent compound, Anhydrite (CaSO 4 ), are investigated within the HF level of theory and two different formulations of hybrid DFT functionals (B3LYP [A. Becke, J. Chem. Phys. 98 , 5648 (1993)] and F 0.6 ‐BLYP [F. Corà et al., Structure and Bonding 113 , 171–232 (2004)]). An external electric field is applied along each of the three periodic lattice vectors of the orthorhombic and hexagonal structures in order to detect the anisotropy of the response. The perturbation introduced by the field is analysed in terms of Mulliken charges and electron density maps. The largest response is due to a polarisation of the covalent SO bonds of the sulfate ions. The high frequency dielectric tensor, ε ∞ , is computed and compared with the experimental value; its anisotropy can be rationalised by the orientation of the sulfate ions relative to the three crystallographic directions. We find that the calculated value of ε ∞ decreases on increasing the percentage of HF exchange in the Hamiltonian; the best match with experiment is given by B3LYP, but a higher percentage of HF exchange is required to reproduce the anisotropy in ε ∞ , a feature that we attribute to the better representation of the equilibrium geometry and bond distances in the latter case. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)