Large second harmonic generation of LiCs2PO4 caused by the metal-cation-centered groups

TL;DR

This study reveals that the large second harmonic generation in LiCs2PO4 is primarily due to metal-cation-centered groups, challenging previous models that emphasized nonmetal groups.

Contribution

The paper introduces a first-principles method to analyze atom-specific contributions to SHG, highlighting the dominant role of metal-cation groups in LCPO.

Findings

SHG response dominated by CsO6 and LiO4 groups

SHG coefficients mainly influenced by O-2p, Cs-5p, Cs-5d, and Li-2p orbitals

Occupied and unoccupied orbitals both crucial for SHG response

Abstract

We evaluated the individual atom contributions to the second harmonic generation (SHG) coefficients of LiCs2PO4 (LCPO) by introducing the partial response functionals on the basis of first principles calculations. The SHG response of LCPO is dominated by the metal-cation-centered groups CsO6 and LiO4, not by the nonmetal-cation-centered groups PO4 one expects from the existing models and theories. The SHG coefficients of LCPO are determined mainly by the occupied orbitals O-2p and Cs-5p as well as by the unoccupied orbitals Cs-5d and Li-2p. For the SHG response of a material, the polarizable atomic orbitals of the occupied and the unoccupied states are both important.