Periodic ab initio calculations of the spontaneous polarisation in ferroelectric NaNO2
2002 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 4, no 17, 4204-4211 p.Article in journal (Refereed) Published
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.
Place, publisher, year, edition, pages
2002. Vol. 4, no 17, 4204-4211 p.
hartree-fock, spontaneous polarization, sodium-nitrite, electronic-structure, deformation density, optical-properties, phase, crystals, charge, knbo3
IdentifiersURN: urn:nbn:se:kth:diva-21833ISI: 000177527500018OAI: oai:DiVA.org:kth-21833DiVA: diva2:340531
QC 201005252010-08-102010-08-10Bibliographically approved