The Optical Conductivity for a Spin-Peierls Ground State of $$hbox {(TMTTF)}_{2}hbox {PF}_{6}$$ (TMTTF) 2 PF 6 with Tetramer Formation

We theoretically investigate the optical conductivity of $$\hbox {(TMTTF)}_{2}\hbox {PF}_{6}$$ in the spin-Peierls ground state within the framework of the exact diagonalization method at absolute zero temperature ( $$T=0$$ ). As an effective model, a 1/4-filled 1D (one-dimensional) extended Hubbard model with tetramerization is employed. Using appropriate parameters of the model which have already been reported, we clarify the electronic photoexcitation energies from the spin-Peierls ground state. Since some experiments indicate the formation of a tetramer in the spin-Peierls ground state of $$\hbox {(TMTTF)}_{2}\hbox {PF}_{6}$$ , our results are useful to understand the effects of tetramerization on the optical properties of $$\hbox {(TMTTF)}_{2}\hbox {PF}_{6}$$ .