Title: A comparative study of different exchange-correlation functionals in understanding structural, electronic and thermoelectric properties of Fe$_{2}$VAl and Fe$_{2}$TiSn compounds,
Abstract: Fe$_{2}$VAl and Fe$_{2}$TiSn are full Heusler compounds with non-magnetic
ground state. The two compouds are good thermoelectric materials. PBE and
LDA(PW92) are the two most commonly used density functionals to study the
Heusler compounds. Along with these two well studied exchange-correlation
functionals, recently developed PBEsol, mBJ and SCAN functionals are employed
to study the two compounds. Using the five functionals equilibrium lattice
parameter and bulk modulus are calculated. Obtained values are compared with
experimental reports wherever available. Electronic structure properties are
studied by calculating dispersion curves, total and partial density of states.
For Fe$_{2}$VAl, band gap of 0.22 eV is obtained from the mBJ potential which
is in reasonable agreement with experimental value while, for Fe$_{2}$TiSn band
gap of 0.68 eV is obtained. Fe$_{2}$VAl is predicted to be semimetallic with
different values of negative gaps from LDA,PBEsol,PBE and SCAN functionals.
Whereas, Fe$_{2}$TiSn is found to be semimetallic(semiconducting) from
LDA,PBEsol(PBE,SCAN) functionals employed calculations. From the dispersion
curve effective mass values are also computed to see the contribution to the
Seebeck coefficient. In Fe$_{2}$TiSn, a flat band is present along the
$\Gamma$-X direction with calculated value of effective mass $\sim$36 more than
the mass of electron. The improvements or inadequacies among the functionals in
explaining the properties of full Heusler alloys for thermoelectric application
are thus observed through this study.