| Self-consistent-variation ground states of a finite-length PtCl complex were obtained in the framework of Baeriswyl-Bishop(BB) model. Proper end values were chosen for fixed-end boundary condition, and suitable end-revision-term was added to the original Hamiltonian for free-end boundary condition. In the two cases, the numerical solutions, both geometrical and electronic structures are similar to those in the Born-Karman condition respectively. No end collapses, and no defective levels in the gap. It shows that the parameter (=18eV/nm) in the end-revision-term is chosen appropriately. And it is also found that the gap absorption peak and the parameter are independent of the length of the PtCl complex.A self-trapped exciton in an open chain with finite length of a PtCl complex was numerically investigated. The results show that the zero-field absorption peak of the exciton is near 1.55eV, which is in good agreement with the recent data observed by Wada et al. In addition, the behaviors of the PtCl exciton in an applying electrostatic field were numerically explored. We came to the results that electric field has strong and interesting effects on the PtCl exciton. No dramatic polarization of the exciton is seen in weak electric field. But in the moderate electric field 150 kV/cm, there is a sharp change in the configuration and charge distribution of the exciton, i.e. the exciton is directly split into an electron polaron and a hole polaron. The polarization and dissociation happen at a same time, which differs from that in conjugated polymers. And in the strong electric field 350 kV/cm, appear structural phase transition of the chain and luminescence quenching.
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