Evaluating Seebeck coefficient of Na xCoO 2 from molecular orbital calculations

Abstract

We propose the evaluations of Seebeck coefficient of Na x CoO 2 ( x = 0.38, 0.67, 0.76, 0.86, and 0.95) systems by Boltzmann theory: Mott expression and Fermi energy from the discrete variational (DV)-Xα molecular orbital calculation. This approach was based on molecular orbital calculations using the Na 8Co 21O 72, Na 14Co 21O 72, Na 16Co 21O 72, Na 18Co 21O 72, and Na 20Co 21O 72 clusters to obtain the Fermi energy at the Co3d orbital of Na x CoO 2 metallic for evaluating the temperature dependence of Seebeck coefficient values. The evaluated Seebeck coefficient of the Na x CoO 2 systems increases with increasing temperature as well as with increasing x value and temperature.