  We report the first principles study of structural, elastic, electronic,
optical and thermoelectric properties of newly synthesized K2Cu2GeS4. The
structural parameters are found to be in good agreement with experimental
results. The single crystal elastic constants (Cij) are calculated and
K2Cu2GeS4 is found to be mechanical stable. The analysis of polycrystalline
elastic constants reveals that the compound is expected to be soft in nature.
The values of Pugh and Poisson ratios suggested that the compound lies in the
border line of ductile/brittle behavior. The chemical bonding is primarily
ionic, the inter-atomic forces are central in nature and the compound is
mechanically anisotropic. The computed electronic band profile shows
semiconducting characteristics and the estimated band gap is strongly dependent
on the functional used representing the exchange correlations. The nature of
chemical bonding is explained using electronic charge density mapping.
Important optical constants such as dielectric constants, refractive index,
absorption coefficient, photoconductivity, reflectivity and loss function are
calculated and discussed in detail. Optical conductivity is found to be in good
qualitative agreement with the results of band structure calculations. The
Seebeck coefficients are positive for the entire temperature range used in this
study, suggesting the presence of p-type charge carriers. We have obtained
large Seebeck coefficent, 681 V/K at 100 K and 286 V/K at 300 K. At room
temperature, the electrical conductivity and electronic thermal conductivity
are 1.8 31018 ms)-1 and 0.5 1014 W/mK.s, respectively. The dimensionless figure
of merit of K2Cu2GeS4 is evaluated as ~1.0 at 300 K. This suggests that
K2Cu2GeS4 is a potential candidate for thermoelectric applications.
