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<p>In the framework of the density functional theory with gradient functionals PBE and PBEsol in the basis of localized orbitals of the CRYSTAL package, ab initio studies of the crystal structure, electronic structure, vibrational spectra and linear, and nonlinear optical coefficients of crawfordite Na<sub>3</sub>Sr(PO<sub>4</sub>)(CO<sub>3</sub>) under pressure are performed. In this structure, sodium and oxygen atoms occupy nonequivalent positions, and it leads to their different charge states and different strengths of chemical bonding in anions [PO<sub>4</sub>]<sup>−2.29</sup> and [CO<sub>3</sub>]<sup>−1.49</sup>, as well as a special structure of the upper valence and lower unoccupied bands. The vibrational modes of the anions dominate in the spectra of infrared absorption and Raman scattering. Under pressure, the refractive indices increase, while the second harmonic generation efficiency becomes less than 0.67×KDP. The structure and properties of designed Na<sub>3</sub>Pb(PO<sub>4</sub>)(CO<sub>3</sub>) crystal with a crawfordite structure, in which the SGH efficiency is 2.3 times greater than that of KDP, are calculated.</p>

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Effects of pressure on structural, electronic and optical properties of noncentrosymmetric monoclinic Na3Sr(PO4)(CO3) with discrete [PO4] and [CO3] units

  • 期刊论文

  • 发表日期：

    2026年1月5日

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  • Yurii Zhuravlev,
  • Victor Atuchin

摘要

In the framework of the density functional theory with gradient functionals PBE and PBEsol in the basis of localized orbitals of the CRYSTAL package, ab initio studies of the crystal structure, electronic structure, vibrational spectra and linear, and nonlinear optical coefficients of crawfordite Na3Sr(PO4)(CO3) under pressure are performed. In this structure, sodium and oxygen atoms occupy nonequivalent positions, and it leads to their different charge states and different strengths of chemical bonding in anions [PO4]−2.29 and [CO3]−1.49, as well as a special structure of the upper valence and lower unoccupied bands. The vibrational modes of the anions dominate in the spectra of infrared absorption and Raman scattering. Under pressure, the refractive indices increase, while the second harmonic generation efficiency becomes less than 0.67×KDP. The structure and properties of designed Na3Pb(PO4)(CO3) crystal with a crawfordite structure, in which the SGH efficiency is 2.3 times greater than that of KDP, are calculated.