Tailoring thermopower of single-molecular junctions by temperature-induced surface reconstruction*

Recent experiments revealed that surface reconstruction occurs at around 300-400K in the interface of C$_{60}$ adsorbed on Cu(111) substrate by scanning tunneling microscope techniques. To understand effects of such reconstruction on thermopower, we investigate the Seebeck coefficients of C$_{60}$ single-molecular junctions without and with surface reconstruction as a function of temperature at different tip-to-molecule heights from first-principles. Our calculations show that surface reconstruction can enhance or suppress Seebeck coefficients according to junctions at different tip heights. We further observe that the Seebeck coefficient of the junction at $d =$3.4{\AA} may change from p- to n-type under surface reconstruction.