The optical absorption spectra and excitonic properties of poly($p$-phenylene vinylene) (PPV) polymers are investigated using first-principles $\mathit{GW}$ and $\mathit{GW}$ plus Bethe-Salpeter equation ($\mathit{GW}$-BSE) method. The calculated optical absorption spectra show much improved agreement with experiment than previous theoretical $\mathit{GW}$-BSE studies. However, we observe a discrepancy in the relative intensity of the two most dominant peaks in the absorption spectra between experimental measurements and calculations, which is caused by the suppression of coherent formation of certain exciton states by the finite chain length of the crystalline PPV samples. The absorption spectra calculated by $\mathit{GW}$-BSE are also shown to be weakly dependent on the mean-field density functional theory (DFT) starting points.

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• Bethe-Salpeter equation
• Excitons
• First-principles calculations
• Optoelectronics
• Polymers
• GW method