Phonon dispersion in poly(dimethylsilane)

In the present communication we report normal modes and their dispersion in polydimethylsilane (PDMS) [–Si(CH3)2–]n using Urey–Bradley force field, which in addition to valence force field accounts for the non-bonded interactions in the gem and cis configurations and tension terms. The partially deuterated PDMS (PDMS-d3), i.e., (SiCH3CD3)n and fully deuterated PDMS (PDMS-d6), i.e., (SiCD3CD3)n are also studied to check the assignments and validity of the force field. Dispersion curves show two interesting features: (1) a divergence of dispersion curves following repulsion of species belonging to the same symmetry; (2) crossing between the two modes. In addition, heat capacity as a function of temperature via density-of-states is evaluated and some of the modes left unassigned by the earlier workers have been assigned.

Graphical abstractIn the present communication we report normal modes and their dispersion in polydimethylsilane (PDMS) [–Si(CH3)2–]n using Urey–Bradley force field, which in addition to valence force field accounts for the non-bonded interactions in the gem and cis configurations and tension terms. The partially deuterated PDMS (PDMS-d3), i.e., (SiCH3CD3)n and fully deuterated PDMS (PDMS-d6), i.e., (SiCD3CD3)n are also studied to check the assignments and validity of the force field. Dispersion curves show two interesting features: (1) a divergence of dispersion curves following repulsion of species belonging to the same symmetry; (2) crossing between the two modes. In addition, heat capacity as a function of temperature via density-of-states is evaluated and some of the modes left unassigned by the earlier workers have been assigned.Figure optionsDownload full-size imageDownload as PowerPoint slide