Vibrational mode frequencies of H2S and H2O adsorbed on Ge(0 0 1)-(2 × 1) surfaces

The equilibrium geometry and vibrational modes of H2S and H2O-terminated Ge(0 0 1)-(2 × 1) surfaces are calculated in a supercell approach using first-principles density functional theory in the local density (LDA), generalized gradient (GGA) approximations and van der Waals (vdW) interactions. Mode frequencies are found using the frozen phonon method. For the H2S-passivated surface, the calculated frequencies in LDA (GGA) are 2429 cm−1 (2490) for the HS stretch mode, 712 cm−1 (706) for the HS bond bending mode, 377 cm−1 (36) for the GeS stretch mode and 328 cm−1 (337) for HS wag mode. Frequencies for the H2O passivated surface are 3590 cm−1 (3600) for the HO stretch mode, 921 cm−1 (947) for the bending mode, 609 cm−1 (559) for the GeO stretch, 1995 cm−1 (1991) for the GeH stretch mode, 498 cm−1 (478) for the GeH bending mode and 342 cm−1 (336) for the HO wag mode. The differences between the functionals including vdW terms and the LDA or GGA are less than the differences between LDA and GGA for the vibrational mode frequencies.