Real-space force constants for lattice dynamics in silicon and germanium in the adiabatic bond-charge model

We investigate in this work the main features of both interplanar and interatomic force constants in silicon and germanium in real space; this study is based on the deconvolution of the adiabatic bond-charge model. Our results for the interplanar force constants are compared to existing first-principles calculations: Very good agreement is found for Ge. As for the interatomic force constant, we find very long-range interactions propagating mostly along (110) planar bonding chains. We confirm therefore the physical importance of these chains, recently suggested by Kane on the basis of different arguments.