Dielectric properties of carbon-, silicon-, and germanium-based polymers: A first-principles study

Abstract

A knowledge of factors that control the electronic structure and dielectric constant of materials would be valuable in the design of new insulators with attractive dielectric properties. In an attempt to systematically and directly understand the role of chemical composition and atomic configuration in determining such properties, we have studied (using first-principles computations) nine homopolymer systems based on $XY$${}_{2}$ building blocks, where $X=\mathrm{C}$, Si, or Ge and $Y=\mathrm{H}$, F, or Cl. Two possible generic configurations were explored, and our computations utilized dispersion-corrected semilocal exchange-correlation functionals as well as hybrid functionals. Correlations between stability, electronic structure features, infrared intensities, and the dielectric response are established across the chemical and configurational space considered. Homopolymers containing GeF${}_{2}$ or GeCl${}_{2}$ building blocks are identified as particularly promising. These systems display large dielectric constant values (regardless of the underlying crystal structure) and may display a large band gap for particular configurations. The design of a polymer insulator with optimal dielectric constant and band gap may require consideration of heteropolymers (e.g., involving CH${}_{2}$ and GeF${}_{2}$ building blocks). We provide a convenient strategy for the rapid exploration of that extended chemical and configurational space.