Shell Model Study of Local and Global Energy Barriers in KDP

S. KOVAL; J. LASAVE; J. KOHANOFF; R. MIGONI

FERROELECTRICS

TAYLOR & FRANCIS LTD

Año: 2010 vol. 401 p. 103 - 109

0015-0193

We perform a study of the energetics of KH2PO4 (KDP) by using a shell model (SM)which was constructed by adjusting the interaction parameters to ab initio calculations,and was fitted to reproduce phonons, polarization-inversion energies and structuralproperties. We calculate the energy profiles by performing global displacements andlocal distortions following the ferroelectric (FE) mode pattern in clusters of differentsizes embedded in a paraelectric (PE) phase matrix. These properties are expected tobe relevant to the PE-FE phase transition. The obtained SM results are compared tocorresponding ab initio (AI) data. The global instabilities are found in good agreementfor both KDP and DKDP. We also find qualitative good agreement in the KDP structureand even quantitative agreement in the expanded DKDP structure for the local distortions.The SM results reproduce well different trends like increasing instabilities as thecluster sizes grows, as the heavier atoms are included, and as the volume is increased,in accordance with the corresponding data from AI calculations.