We present a theoretical study of the electronic structure, surface energies and work functions of orthorhombic Pt monosilicide and germanides of Pt, Ni, Y and Hf within the framework of density functional theory (DFT). Our calculated bulk structures are within 1-2% of reported experimental values. Calculated work functsions for the (001) surfaces of PtSi, NiGe and PtGe are 5.12, 4.57 and 4.83 eV, respectively, suggesting that these metals and their alloys can be used as self-aligned contacts to p-type silicon and germanium. Work functions for Y and Hf germanides range from 2.4 to 4.3 eV making them a possible n-type contact material. In addition, we also report an ab-initio calculation of the Schottky-barrier height at the Si(001)/PtSi(001) interface. The p-type Schottky barrier height of 0.28 eV is found in good agreement with predictions of a simple metal induced gap states (MIGS) theory and available experiment. This low barrier suggests PtSi as a low contact resistance junction metal for silicon CMOS technology. We identify the growth conditions necessary to stabilize this orientation.