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  Physics Express 2013, 3: 31
  Research Article
First - principles calculations of electronic structure, optical properties and phase instability of potassium dihydrogen arsenate
  G. Sriprakasha, S. N. Prabhavab, K. P. Rameshc, K. Rukmania  
a Department of Physics, Bangalore University, Bangalore-560056, India
b CeNSE, Indian Institute of Science, Bangalore-560012, India
c Department of Physics, Indian Institute of Science, Bangalore-560012, India

  We have carried out first - principles calculations using density functional theory (DFT) and estimated electronic structure, optical properties and phase instability of tetragonal KDA. Born effective charges (Z*) of different atoms in potassium dihydrogen arsenate (KDA) and potassium dihydrogen phosphate (KDP) have been evaluated and it is found that the zz component of Z* for arsenic is smaller than that of phosphorous indicating the low contribution to the dipole moment due to distortion of AsO4 ion compared to that of PO4 ion. The reasons for deviation from linear relation between O-H--O bond distance (R) and Tc have been discussed. The negative phonon frequencies (B2 and E) reveal instability of the tetragonal KDA. The Raman frequencies obtained from of density functional perturbation theory (DFPT) calculations are found to be in very good agreement with experimental data. The calculations made considering the pressure effect on KDA show the absence of unstable modes confirming the validity of DFPT.
  Electronic states; Reflectivity spectra; Born effective charge tensor; Phonon frequencies  

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