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  • Quasiparticle and excitonic...
    Mostaani, E; Monserrat, B; Drummond, N. D; Lambert, C. J

    Physical chemistry chemical physics : PCCP, 06/2016, Letnik: 18, Številka: 22
    Journal Article

    We report diffusion quantum Monte Carlo (DMC) calculations of the quasiparticle and excitonic gaps of hydrogen-terminated oligoynes and extended polyyne. The electronic gaps are found to be very sensitive to the atomic structure in these systems. We have therefore optimised the geometry of polyyne by directly minimising the DMC energy with respect to the lattice constant and the Peierls-induced carbon-carbon bond-length alternation. We find the bond-length alternation of polyyne to be 0.136(2) Å and the excitonic and quasiparticle gaps to be 3.30(7) and 3.4(1) eV, respectively. The DMC zone-centre longitudinal optical phonon frequency of polyyne is 2084(5) cm −1 , which is consistent with Raman spectroscopic measurements for large oligoynes. The charge density of a one-dimensional sp-bonded chain composed of 26 carbon atoms terminated by H with alternating single and triple bonds.