BeGeN2

Contents

Crystal Structures

Space Group: Pbn2₁NOTE: see discussion of crystal structures

_{Point Group}_{: C}_2v

_{Lattice constants}_:

_{Note: we use the a>b>c choice discussed in the section "Crystal Structures". In the references, a and b are interchanged.}

Wyckoff positions: from [3]

Electronic band structure

The band gap is direct at the Γ- point.

Band Gaps:

Figure 1: Band structure of BeGeN₂ calculated by the FLAPW

method with GGA. [1]

Figure 2: Band structure of BeGeN₂in the QSGW method from [3]. One can zoom in to the range of k and E

of interest.

Elastic Properties

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Vibrational Properties

Phonon frequencies at Γ in cm^-1 [4]

Raman spectra for different scattering geometries and infrared spectra for different polarizations can be found in [4]

Born effective charges can be found in [4]

Phonon dispersion curves and DOS can be found in [4]

Optical Properties

Dielectric Constants (at high frequency, electronic screening only, from DFT-LDA calculations)

ε_xx= 4.75 ε_yy = 4.72 ε_zz = 4.90 [2]

ε_xx= 4.91 ε_yy = 4.97 ε_zz = 5.14 [4]

Index of refraction [4]

n_x= 2.22 n_y=2.23 n_z=2.27

Figure 3: Real (ε₁) and imaginary (ε₂) parts of the dielectric function versus photon energy for

BeGeN₂ for different light polarizations, calculated by FLAPW with GGA. [1]

Second order nonlinear optical coefficients (units pm/V)

χ _zzz=-18.14 χ _xzx = χ _zxx =6.22 χ _yzy = χ _zyy = 3.47

Optical dielectric functions ε₂(ω)andε₁(ω) are reported in [2] for each direction based on GGA calcs., and shown in Fig. 2.

Dielectric Properties

Static dielectric constants [4]

ε_xx⁰ = 8.94 ε_yy⁰ = 9.40 ε_zz⁰ = 10.19

_References

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