Figure 1

(Color online) (a) The structure of the orthorhombic $Pmm2\beta \text{-PVDF}$ cell with two VDF monomers. Extra monomers are shown to illustrate how the all-trans polymer chains are formed by applying the PBC along the $y$ direction. (b) The sketch of a positive octant of the $Pmm2$ BZ referred to the same coordinate axes as in (a). [(c) and (d)] The $n=4$ oligomer systems with the OH- bottom and ${\text{CF}}_3\text{−}$ and ${\text{CH}}_3\text{−}$ top anchoring units. H and C atoms are represented by small white and black spheres, respectively. F atoms are represented by large spheres of two different shades to better distinguish individual oligomer chains.Reuse & Permissions

Figure 2

(Color online) (a) Dispersion of the phonon bands in the 12-atom orthorhombic $\beta \text{-PVDF}$ unit cell along the symmetric directions in the $Pmm2$ BZ, outlined in Fig. 1b. High-frequency bands in the vicinity of $3000{\text{cm}}^{-1}$ are not shown. [(b) and (c)] Sketches of the VDF monomer tilting patterns produced by freezing-in of the (b) $Y_1$ and (c) $Y_2$ structural instabilities, viewed along the backbone $\left(y\right)$ direction. Color conventions are the same as for Fig. 1. (d) Dispersion of the phonon bands for the relaxed cell-doubled $Ama2\beta \text{-PVDF}$ crystal with the frozen-in $Y_1$ structural instability. Only the low-frequency bands are shown. In the panels (a) and (d), dots placed along the frequency axis at $\Gamma$ point indicate phonon frequencies computed with vanishing LO-TO splitting. All the phonon frequencies shown here were rescaled with an empirical factor. See text for more details.Reuse & Permissions

Figure 3

(Color online) Comparison of simulated and experimental IR spectra for the $n=6$ OVDF structure, terminated with ${\text{CF}}_3\text{−}$ on one end and either OH (simulated) or iodine (experimental) on the other. All spectra are normalized to the strongest peak and shifted for clarity. (a) Experimental spectrum, (b) crystal calculation with QE, and (c) isolated-chain calculation with PQS.Reuse & Permissions