Scanning tunneling microscopy of binary alloys: first principles calculation of the current for PtX (100) surfaces

To probe the influence of realistic tip models on the tunnel current and the corrugation of binary alloy surfaces we have calculated the electronic structure of PtX (100) sample surfaces and realistic STM tips with different tip atoms. We then used the Bardeen integral to calculate the tunnel current from the electronic structure of sample and tip numerically. Apart from the usual approximations of the perturbation approach the method developed is therefore fully ab initio. It can be shown that the currents obtained in the limit of low bias voltage are within the range of measurements, and equally, that including a realistic tip improves the agreement between measurements and calculations.