Alfredsson, M. and Hermansson, K. and Dovesi, R. (2002) Periodic ab initio calculations of the spontaneous polarisation in ferroelectric NaNO2. Physical Chemistry Chemical Physics, 4 (17). pp. 4204-4211. ISSN 1463-9076.
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We present periodic ab initio calculations for ferroelectric NaNO2. The spontaneous polarisation (P-s) has been calculated with three different models based on: (i) point charges; (ii) a multipolar expansion of the charge ;distribution; and (iii) the Berry phase approach. Both the Hartree-Fock and LDA Hamiltonians were employed. Within the Hartree-Fock scheme, at the optimised geometry, we obtain P-s values of 20.3, 13.0 and 16.4 muC cm(-2) with the three models, compared to the experimental value of similar to11.9 muC m(-2). The Berry-phase approach at the Hartree-Fock level gives a value very close to experiment ( namely 12 muC cm(-2)) when the experimental structure is used. At the optimised LDA structure, the LDA P-s values are 16.8, 10.0 and 16.9 muC cm(-2) with models (i)-(iii). The optimised lattice parameters at the Hartree-Fock level are slightly shorter (between 0 and 4%) than those determined experimentally from X-ray-diffraction, while the lattice parameters of the LDA-optimised structure are up to 10% smaller than the experiment. The calculated lattice energies are 679 and 964 kJ mol(-1) at the HF and LDA levels, compared with 729 kJ mol(-1) from the experiment. Charge densities, Mulliken charges and dipole moments are discussed. Finally, we have studied the mechanism for the phase transformation in-between the ferroelectric and paraelectric crystal structures; a rotation of the NO2 group around the c-axis gives the lowest energy barrier.
|Additional information:||ISI Document Delivery No.: 585MA Times Cited: 2 Cited Reference Count: 47|
|Divisions:||Faculties > Science Technology and Medical Studies > School of Physical Sciences > Functional Materials Group|
|Depositing User:||Maria Alfredsson|
|Date Deposited:||04 Sep 2008 16:33|
|Last Modified:||14 Jan 2010 14:17|
|Resource URI:||http://kar.kent.ac.uk/id/eprint/4766 (The current URI for this page, for reference purposes)|
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